Skin Basics
Our skin is the heaviest and largest organ of the body, weighting as much as 10 kg and having a surface of up to 1 square metres – all while being only a few millimetres deep.
Our skin has multiple functions, but its primary role is to serve as protection from the world outside of our body. For example, our skin prevents harmful pathogens from entering our body, and it protects us from potentially harmful abiotic factors, like sun rays. Our skin is also an important regulator of body temperature, and it allows our body to feel sensations like warmth, cold, pressure, itching and pain. The skin also helps maintain optimal levels of moisture inside our body, protecting us from dehydration and serves as a storage for water, fat and metabolic products.
- The epidermis is primarily made up of cells that produce keratin, called keratinocytes. Other cell types found on the epidermis are:
- Melanocytes – these cells produce and store a black pigment called melanin that protects the skin from UV rays.
- Lymphocytes and Langerhans cells – these cells fight off germs by taking them to the nearest lymph node, where they are eliminated.
- Merkel cells – these are a special type of nerve cells that allows you to sense pressure.
- The dermis is mostly composed of collagen fibres, which make skin strong and flexible. The dermis also contains nerve cells and small blood vessels, called capillaries, which transport nutrients and oxygen to cells. Capillaries also help the skin cool down. In this layer, there are also sensory cells and sweat glands.
- The Subcutis is the deepest skin layer, also known as hypodermis, and it is made up mostly of fat and connective tissue. The hypodermis provides insulation and cushioning to the body beneath. This layer also contains blood vessels and lymph vessels, as well as nerves, sweat glands, oil glands, scent glands and hair roots.
- The epidermis is primarily made up of cells that produce keratin, called keratinocytes. Other cell types found on the epidermis are:
Our skin is a vital organ of our body and it susceptible to multiple factors that can cause disease or malfunction, potentially affecting our overall health. For example, some common diseases of the skin include acne, psoriasis, atopic dermatitis, eczema, tinea versicolor, seborrheic dermatitis, rosacea, vitiligo, warts, and blepharitis.
Certain conditions can also make your skin more attractive to mosquitoes, potentially increasing your chances of catching certain diseases, like malaria.
Skin Health
Having healthy skin depends on various factors, like your diet, hormone levels, hygiene, and the composition of your skin microbiota.
Skin health reflects the health of a large number of systems in the body involving hormones. For example, alterations to the optimal functioning of the hypothalamic-pituitary axis, thyroid gland, pancreas, adrenal gland, and the androgen signalling axis are associated with specific conditions that manifest in the skin. For a comprehensive review, see this article.
- following a diet rich in micronutrients like vitamins and minerals is essential to maintain a healthy skin. For example,
- Vitamin A
- Regulates the proliferation of epidermal keratinocytes and dermal fibroblasts (Varani et al., 1994)
- Prevents skin damage from UV irradiation (Fisher et al., 1997)
- Vitamin C
- Suppresses production of free radicals from UV exposure, protecting cells from oxidative stress (McArdle et al., 2002)
- Reduces damage to the skin by UV irradiation (McArdle et al., 2002; Stewart et al., 1996)
- Promotes wound healing (Fisher et al., 1996)
- Improves skin hydration (Campos et al., 2008)
- Vitamin D
- Improve innate immunity (through stimulation of cathelicidin antimicrobial peptide production) (Gombart et al., 2005)
- Modulates inflammation, angiogenesis, wound healing (Frohm et al., 1997; Koczulla et al., 2003)
- Vitamin E
- Suppresses lipid peroxidation (Lopez-Torres et al., 1998)
- Modulates photoaging (Bissett et al., 1990; Jurkiewicz et al., 1995) and photocarcinogenesis (Burke et al., 2000)
- Exhibits anti-inflammatory roles (Meydani et al., 1990; Wu et al., 2008)
- Zinc
- Protects from photodamage (Mitchnick et al., 1999)
- Exhibits antimicrobial activity (Mitchnick et al., 1999)
- Copper
- Serves as an antioxidant (Pickart et al., 2012)
- Stimulates the maturation of collagen (Pickart, 2008)
- Modulates melanin synthesis (Menkes, 1988)
- Selenium
- Protect skin from UV irradiation-induced oxidative stress (Balagopalakrishna et al., 1997; Rafferty et al., 1998)
- Useful for the prevention and treatment of psoriasis (Juhlin et al., 1982)
Micronutrient deficiencies can easily occur if you are not mindful of your diet and follow at high sugar, high fat diet, low in fruits and vegetables. Such diet can lead to various skin diseases, including:
(Mihaly et al., 2011);
Delayed wound healing (Hunt, 1986) – linked to deficiency in vitamin A. Vitamin A is also important for the prevention and treatment of psoriasis (Jean et al., 2011; van de Kerkhof, 2006), ichthyosis (van Steensel, 2007), skin cancer (Niles, 2002), and acne (Kligman, 1997).(Mihaly et al., 2011);
Thickening of the stratum corneum, and delayed wound healing in scurvy (Hodges et al., 1971) – linked to a deficiency in vitamin C.
Associated with low levels of (Mesquita Kde et al., 2013; Peroni et al., 2011)
(Igarashi et al., 1989, Machlin et al., 1977) – is linked to low levels of vitamin E.
Associated with low zinc levels (Fine et al., 1989, Ewing et al., 1991).
Linked to copper deficiency (Menkes, 1988)
are linked to abnormal selenium levels (Juhlin et al., 1982; Naziroglu et al., 2012; Fine et al., 2008; McKenzie, 2000).
Hygiene
Another important factor affecting skin health is hygiene. While our skin serves as a formidable barrier against pathogens, basic hygienic practices are important to prevent infections. Exposure to potential pathogens, for example, can easily occur through your hands, which are constantly exposed to new surfaces. Hence, it is important to follow optimal hygienic practices that keep your hands clean. However, care should be taken on the excessive use of hand sanitizers and other chemicals meant to kill bacteria, due to the risk of favouring the development of antibiotic-resistant bacterial strains.
Skin Microbiota
The skin is home to multiple species of microorganisms, including bacteria and fungi, which are distributed across different skin locations. The composition and richness of these microbes depends on the physical properties of each skin site. Studies have shown that specific types of bacteria are associated with moist, dry and sebaceous (oily) skin microenvironments.
Today, more and more researchers and clinicians are considering the skin microbiota when assessing a skin disease. Why should you consider the skin microbiota when thinking about your skin disease? Because skin microbes may be influencing your condition. In recent years multiple studies have identified potential roles for different skin microbes in a wide range of skin diseases, from the common acne to conditions like vitiligo.
FOCUS ON: SKIN MICROBIOTA
THE SKIN ECOSYSTEM
Our skin is a unique organ. Not only is it the largest and heaviest organ, but it is also the most diverse. The skin is, overall, cool, acidic and dry, but different parts of the skin have distinct properties, some sections are dryer than others, whereas some bits are oily, and all across the skin has different thickness, folds and density of hair follicles. Another unique property of the skin: it is a continuously self-renewing organ, with skin cells being constantly shed and replaced in the epidermis, the outermost layer of skin.
Our skin is also an ecosystem, inhabited by the multiple species of microorganisms that make up the skin microbiota, living in different parts of the skin. This skin microbiota is acquired early in our life, possible even before we are born.
SKIN MICROBIOME FROM BIRTH TO ADULTHOOD
Our body’s microbiota, including the microbiota of our skin, is initially formed by exposure to our mother’s microbes, transferred over our body when we are born. In fact, some studies suggest that even before we are born, we receive some microbes from our mum (Tamburini 2016, Nuriel-Huayon 2016, Younge 2019).
One important factor that defines the early composition of the skin microbiota is the type of birth and whether a baby is breastfed. Babies born through natural birth are exposed to the microbes found in their mother’s skin and vaginal canal, including bacteria such as Lactobacillus, Prevotella, Bifidobacterium and Bacteroides.
Among these bacteria, species of the Lactobacillus group have been identified as being a critical member of a healthy vaginal microbiota, as well as having an important role in the normal progression of birth. Bacterial vaginosis, for example, is commonly associated with low levels of Lactobacillus species, which allow for the establishment of potentially harmful species, such as Gardnerella, Atopobium, Mobiluncus, Prevotella, Streptococcus, Mycoplasma, Ureaplasma, Dialister, and Bacteroides (Amabebe 2018).
In contrast to normal birth, studies have shown that babies born from C-section are colonized by different microbial species, including species from the microbial genera such as Staphylococcus, Propionibacterium or Clostridium. More importantly, studies have shown that several early life factors like the type of birth, diet, exposure to antibiotics, hygiene, and the use of prebiotic or probiotic supplements can also influence the composition of a baby’s microbiome.
For more information about human microbes during our first years of life, please read our article on Babies, Microbes and Health.
GEOGRAPHY OF THE SKIN MICROBIOTA
The composition and diversity of these microbes is determined by the specific physical properties of each skin region (Figure 1). For example,
include the forehead, retroauricular crease (behind the ears), the back, and the alar crease (side of the nostril). These sites host reduced levels of bacterial diversity, compared to other skin sites and the five most common bacterial species include Propionibacterium acnes, Staphylococcus epidermidis, Corynebacterium tuberculostearicum, Staphylococcus capitis and Corynebacterium simulans.
Include the skin of the forearms, palm, and buttocks. These dry skin patches are populated by multiple bacterial species, from which the five most common are Propionibacterium acnes, Corynebacterium tuberculostearicum, Streptococcus mitis, Streptococcus oralis and Streptococcus pseudopneumoniae.
Include places like the belly button, nares, the skin between your fingers and toes, the heel, and a few others (Figure 1). In these moist skin areas, the five most common bacteria are Corynebacterium tuberculostearicum, Staphylococcus hominis, Propionibacterium acnes, Staphylococcus epidermidis and Staphylococcus capitis.
Beyond bacteria, other microorganisms also inhabit your skin, including fungi, viruses and even mites. Some of the most common examples include:
These are the most abundant microorganisms found on the skin, after bacteria. Compared to skin bacteria, fungi are less selective about the skin microenvironment they colonize and are more found across all different skin sites. Among skin fungi, members of the genus Malassezia seems to be the common group. One study found that up to 80% of the total fungal skin population belong to this genus (Gao 2010). Other fungal species reported in the human skin can be found in Table 1.
There is still much to learn about the skin viral microbiome, and there are no studies so far elucidating the composition and abundance of viruses in healthy human skin. So far, we know of some skin viruses that are associated with bacteria, called bacteriophages. So far, studies have not identified a normal viral flora in the normal, healthy human skin, but some viruses have been associated with certain skin disease. For example, the Merkel cell polyomavirus is a known causative agent of a rate form of skin cancer. Other viral species identified in the human skin can be found in Table 1.
Small arthropods of the genus Demodex are common inhabitants of facial skin. These mites are obligated inhabitants of our skin, living inside hair follicles and feeding on our dead skin cells. One species of these mites, Demodex folliculorum is commonly found in facial skin and around the eyes, whereas Demodex brevis can be found across the body. Normally, these mites do not cause any health problems, unless a person suffers from certain skin conditions, like rosacea, a weak immune system or if there is an overgrowth of the mites.
Table 1. Five most common microbes found in the human skin, organised by moist, oily and dry skin sites.
[table id=1 /]
Like all ecosystems, alterations in the equilibrium of skin microbes can lead to health problems, due to the overgrowth of particular species or due to an increased likelihood of pathogen infections.
Skin dysbiosis occur when there is an imbalance in the composition and distribution of the normal skin microbiota. Skin dysbiosis is associated with multiple factors, including multiple skin diseases, environmental exposure to pathogens, antibiotic use, and malfunctions of the immune system.
SKIN MICROBIOTA AND HEALTH
Our skin hosts a rich microbial community, which play different roles in our health. Under optimal conditions, the different microbial species living in your skin are in equilibrium among themselves, keeping their own growth in check, and fighting off invading pathogens7 and influencing different aspects of our health. For example, the skin microbiota is known to be involved with:
- Regulation and promotion of optimal immune function
- Barrier function, preventing the entrance of environmental pathogens
- Maintenance of skin microbial equilibrium, preventing overgrowth of potentially harmful species (skin dysbiosis)
CULTIVATING A HEALTHY SKIN MICROBIOTA
The first step we need to take for keeping a healthy skin microbiota is understanding the many factors involved. Changes in pH, water content, transepidermal water loss, and sebum production can influence the composition of the skin microbiota (Younge 2018). Also, demographic, lifestyle (e.g. diet and exercise), physiological and environmental factors can affect the microbial composition of the skin (Dimitriu 2019).
Under optimal conditions, the skin microbiota (also called skin microbiome) is in a state of equilibrium among the different microbial species inhabiting it. However, sometimes overgrowth of specific resident or foreign microbes occurs, causing disease. Skin dysbiosis occur when there is an overgrowth of specific skin microbes, usually bacteria, leading to an impaired function of the whole microbial ecosystem. But, what causes dysbiosis? Some key findings in this area include:
- Excessive cleansing of the skin can harm your skin and affect your microbial composition. Using harsh cleansers, or excessive scrubbing of the skin can decrease the abundance of normal skin flora and can also cause tears in the skin. Tears in the skin can allow pathogen to enter directly into the bloodstream, causing disease.
- Exposure to a farm environment can affect the skin microbiota in children. One study compared the skin microbiota of children with atopic dermatitis living in a farm setting to children not living in a farm. Their results showed that children who lived in a farm were less likely to suffer from dermatitis. These children also had higher skin microbial diversity and a different microbial composition, compared to children from other settings (Steiman 2018).
- Antibiotic use can cause skin dysbiosis. One study in mice showed that treatment with the antibiotic vancomycin resulted in significant reduction in skin microbiota, particularly affecting bacteria of the genus Staphylococcus. The study also found that the use of this antibiotic led to delayed skin wound repair (Zhang 2015).
- Immune malfunction can lead to an increased propensity of acquiring pathogens from the environment and developing skin diseases (Chovatiya 2018).
- The environment where you live can influence your skin microbiota. Studies have shown, for example, that living near agricultural or forested areas lead to high levels of Proteobacteria in the skin (Von Hertzen 2015). Within a city, living near green spaces, like parks or a garden, can influence the bacteria in your skin and have beneficial effects (Ruokolainen 2015).
- Obesity can influence the composition of your skin microbiota and affect your likelihood of acquiring infections. In one study, obese women who went through caesarean delivery were found to have a significantly different skin microbiota at the site of incision (where the baby is extracted), compared to women with healthy weight. Firmicutes bacteria predominated over Actinobacteria, whereas Clostridales and Bacteroidales predominated over commensal Staphylococcus andPropionbacterium Furthermore, the study found that obese women had a higher likelihood of developing infections at the incision site (Rood 2018).
- The clothes you wear can be a source of chemicals that may affect your health. In a recent review, researchers identified a large number of potential chemicals that could be present in newly purchased clothes, like alkylphenol ethoxylates, phthalate esters, alkyl amines, aniline, pyridine, and quinoline. Pathogenic bacteria, such as Clostridium difficile or vancomycin-resistant Enterococcus have been reported to be found in clothes from health workers. Likewise, direct dispersal of certain bacteria, like Staphylococcus aureus from clothing into air has been reported in various hospital settings.
DISEASES ASSOCIATED WITH SKIN DYSBIOSIS
Skin dysbiosis has been associated with multiple diseases of the skin, including acne, eczema and many others2. Below we describe key facts about some of these conditions.
DRIVING FACTORS
- The bacterium Propionibacterium acnes (also known as Cutibacterium acnes) has a well-known association with the prevalence of acne, especially in teenage years. This bacterial species is also the most abundant microbe within the skin microbiota of healthy adults. However, having these bacteria in your skin does not mean you will develop acne, as only a minority of adults develop acne, despite most of them hosting the bacteria in their skin.
- There is also variation in the type of acne bacteria that lives in your skin. For example, P. acne of the 1A1 subgroup, a kind of subspecies, has been consistently linked to the development of acne (Fitz-Gibbon 2013). Another study, which compared levels of P. acne between healthy and acne patients, found significant differences in the type of bacteria found on each group. People with acne had different strains of the P. acne bacteria, compared to healthy people, hinting at the importance of understanding the bacterial makeup of your skin.
Also known as eczema, is a chronic, inflammatory skin condition that is usually inherited and characterised by the development of dry, itching and reddened patches of skin. Skin affected by eczema is also more likely to pick up bacterial infections like impetigo, as well as viral infections like cold sores and warts. Diagnosis of atopic dermatitis usually requires physical examination of the affected skin, following standard diagnostic criteria for this condition.
DRIVING FACTORS
From a biological perspective, eczema occurs due to the inability to repair damage to the skin barrier. This happens because of mutations affecting the function of a gene called filaggrin, which is involved in skin barrier function. However, genetics is not the only factor involved in the development of this disease, another important contributing factor involve the skin microbiota.
- One study analysed the skin microbiota of children affected by eczema, with the goal of understanding what skin microbes are involved with this condition. The study found that children with eczema had elevated levels of Staphylococcus aureus, compared to healthy participants. Other species of bacteria, like epidermidis also increased in abundance during eczema flares. The study also found the abundance of some skin bacteria was influenced by eczema treatments. Bacterial species from the Streptococcus, Propionibacterium, and Corynebacterium genera increased in abundance following eczema treatment (Kong 2012).
- A recent review on this topic (Thomas 2017) found that other species within the Staphylococcus genus are also involved with the pathogenesis of eczema. The review also reported that variation in the composition of gut microbes can also influence eczema. For example, children and young adults with AD have been shown to have lower concentrations of Bifidobacteria, a common gut bacterial genus. In Japan, the fungal species were found to have an important role in eczema development, particularly the species Malassezia restricta and globosa, which were found in over 90% of patients with eczema.
This is an inflammatory condition of the eye, causing pain and swelling of the eyelids. Common symptoms of blepharitis include itchy and burning sensation in the eyes, watery eyes, excessive blinking, or having crusty or sticky eyelids.
DRIVING FACTORS
- Blepharitis is caused by a microbial infection, involving Demodex mites, which are carriers of bacteria, such as Streptococci, Staphylococci or Bacillus oleronius. These bacteria, along with features of the mites can elicit inflammatory responses in the skin, leading to the development of blepharitis’ symptoms (Liu 2010).
- One study found that people with blepharitis had a particular skin microbial signature, characterised by increased levels of Staphylococcus, Streptophyta, Corynebacterium, and Enhydrobacter, and relatively low levels of Propionibacterium (Lee 2012).
Is a chronic inflammatory skin condition characterised by dry, raised, or red patches of skin covered with silvery scales. It is estimated that more than 11% of the general population of some countries suffers from some form of psoriasis. There are five known forms of psoriasis, but the most common, affecting 90% of patients, is called chronic plaque psoriasis or psoriasis vulgaris.
While psoriasis can occur anywhere in the body, it is more commonly found in knees, elbow and scalp. There are also other symptoms that can occur, including nail discoloration, sores on the chest, arms, legs or scalp, or swollen and painful joints. In rare cases, psoriasis can be present as pus-filled blisters or a rash that itches or burns profusely. Psoriasis is usually diagnosed through a skin examination and through evaluation of a patient’s medical history.
DRIVING FACTORS
Multiple genes have been linked to psoriasis vulgaris development, and most of them involve an altered immune function. It has been shown, for example, that an abnormal immune response to an antimicrobial chemical, called LL-37, is likely linked to the development of psoriasis. This antimicrobial chemical is produced by skin bacteria, hinting at the importance of the skin microbiota on the pathology of this disease.
- Some studies have linked the presence of Staphylococcus aureus, Streptococcus pyogenes, and the fungi Malassezia to worsening cases of psoriasis (Tomi 2005, Raza 2007, Rudramurthy 2014).
- A recent study used genomic sequencing approaches to study the skin diversity in people affected by psoriasis, comparing healthy and affected skin patches (Tett 2017). Their results show skin affected by psoriatic events is characterised by a reduction in microbial diversity, and by an increase in the levels of Staphylococcus Their study also found the existence of unknown, undescribed microbial species, which may also play a role in the pathogenesis of this disease. This finding hint at the need of more research to fully understand the role microbes play in the development of psoriasis.
- Genetic tools have proven useful for the identification of altered skin microbiota that may be driving psoriatic events. In one study, researchers found that using DNA sequencing approaches, it was possible to detect a “DNA signature” of psoriasis, based on the abundance patterns of skin bacteria like Corynebacterium, Propionibacterium, Staphylococcus and Streptococcus (Statnikov 2013). The findings of this study support the value of using genetic testing for evaluating skin health, particularly when psoriasis is suspected.
In other cases, there can be some inherited predispositions to psoriasis, where certain drugs, such as beta blockers, non-steroidal anti-inflammatory medications or antimalarial medication can trigger psoriatic flare ups. Smoking or skin injuries can also worsen your psoriasis.
This is a chronic inflammatory condition, commonly affecting the cheeks, nose and chin and other parts of the face, causing rashes, redness, and flushing. In some cases, pimples and pustules can develop as well. It has been estimated that up to 3% of the world’s population is affected by this condition. Rosacea is usually diagnosed through physical examination and analysis of a patient’s medical history. Blood test might be employed in some cases to rule out other conditions, like lupus erythematosus.
DRIVING FACTORS
While the driving factors of rosacea are not fully understood, some studies suggest there might be a genetic component involved, whereas other studies suggest skin microbes may have an important role.
- Various studies suggest that high density of Demodex mites may be involved in the development of rosacea (Jarmuda 2012). Beyond mites, studies have also linked skin bacteria, such as Bacillus oleroniusand Staphylococcus epidermidis to the development of this condition. The idea being that these bacteria use Demodex mites to move around skin sites.
- In one form of rosacea, called papulopustular rosacea, patients suffer from dry and sensitive skin. A recent study found that a key factor driving this pathology is an abnormal sebaceous fatty acid composition, with reduced levels of long chain saturated fatty acids (Raghallaigh 2012).
This common inflammatory skin condition mostly affects the scalp, causing scaly patches, red skin and dandruff. In infants SD can also lead to cradle cap. Other areas that can be affected by this condition include oily patches of skin, like those found in parts of the face (sides of the nose, eyebrows, ears, eyelids) and chest. Globally, some forms of seborrheic dermatitis are very common, like dandruff, which affects nearly half of the world’s population (Piérard‐Franchimont 2006). Other conditions, like seborrheic dermatitis affect up to 5% of the general population and as much as 33% of all patients with compromised immune systems (Schwartz 2012). SD is normally diagnosed through skin examination and, occasionally, though a biopsy, where skin cells are removed from the affected area and examined under the microscope.
Seborrheic dermatitis is thought to be the consequence of fungi of the genus Malassezia, although the details of how this fungi influences this condition are not fully understood, with some recent studies casting doubts on the role of this fungi (Paulino 2017). A recent study, that analysed the skin microbiota of 24 patients with seborrheic dermatitis found that skin bacteria of the genus Acinetobacter, Staphylococcus and Streptococcus were more common is patients with SD, compared to healthy people (Tanaka 2016).
DRIVING FACTORS
- Neurologic conditions, like Parkinson’s disease or depression have been associated with development of SD.
- A weakened immune system can drive the development of SD, as observed in people who:
- are organ transplant recipients
- have HIV/AIDS, or other immuneweakening conditions,
- have alcoholic pancreatitis
- suffer from some forms of cancer
- are recovering from a heart attack or other medical conditions
- Obesity – one study compared levels of high-density lipoprotein (HDL) between healthy people and patients suffering from seborrheic dermatitis. Their results showed significant differences between the two groups, showing that people with SD had significantly higher HDL levels (Imamoglu 2016).
- Stress and Sleep – Both high levels of stress and sleep deprivation are well known factors that drive the flare-ups of SD.
- Pollution and other environmental contaminants
- Use of certain skin care products containing alcoholPre-existing conditions like acne
Beyond disease, the skin microbiota also influence the production of human body odour. In fact, the human armpit is one of most densely inhabited habitat, and the bacteria living in your armpitmetabolize odorless sweat to malodorous compounds. In particular, human skin microbes may influence a person’s “attractiveness” to mosquitos, which use odour cues to find their target host.
- One study found that people who are naturally attractive to the mosquito Anopheles gambia s.s., had lower skin bacterial diversity and high abundance of particular species (Verhulst 2011). For example, the study found that people who are naturally attractive to mosquitoes had a higher abundance of Staphylococcus spp.
The study also reported that the abundance of Staphylococcus spp. was 2.62 times higher in people who were highly attractive to mosquitoes, compared to people who were poorly attractive to mosquitoes. Likewise, the study found the opposite pattern for abundance of the skin bacteria Pseudomonas spp., which was 3.11 times more abundant in people who naturally repelled mosquitoes, compared to those who attracted them.
This fungal infection is characterised by the development of a rash, particularly on the back, neck, upper chest, shoulders, armpits, and upper arms, and it affect mostly older children and young adults. This condition is caused by Malassezia furfur, a common fungal species of the human skin that doesn’t normally cause health problems (Marcon 1987). However, under certain circumstances, this species can overgrowth, causing this condition. Other fungal species are also known to affect other parts of the body, causing well-known conditions like athlete’s foot, dandruff, jock itch, and nail infections (White 2014). Tinea versicolor is usually diagnosed by direct examination of the skin and occasionally though the use of a black light lamp, such as a wood lamp.
DRIVING FACTORS
- The main factor driving tinea versicolor as well as other forms of tinea is the overgrowth of fungi of the genus Malassezia.
- Other contributing factors that can promote the spread of these fungi on the skin, influencing the pathology of this condition. For example, hot and humid weather, having oily skin, sweating a lot, hormonal dysfunction or having problems with the immune system can all influence the growth of Malassezia on the skin.
- One study found that people suffering from tenia pedis, a condition commonly known as athlete’s foot, had a skin microbiome with reduced microbial diversity (Liu 2019). The skin of this patient was dominated by bacteria of the bacterial Staphylococcus genus and fungi of the genus Trichophyton.
This is a relatively common condition, where pigment-producing cells, called melanocytes, are destroyed, rending the skin unable to produce pigment. As a result, a person with vitiligo has patches of white skin. It is estimated as much as 2% of the world’s population if affected by some form of vitiligo. Diagnosis for vitiligo requires a skin examination and may include a blood test to check for autoimmune conditions.
DRIVING FACTORS
So far, it remains unknown what causes vitiligo, but the leading hypothesis points towards an autoimmune disorder, suggesting that this condition may be inherited and involve genetic alteration at immune genes. However, other studies have identified a potential role for skin microbes.
- One study examined the skin microbiota of vitiligo patients and found evidence of skin microbial dysbiosis. All patients examined showed alterations in the composition of skin microbiota in skin patches affected by vitiligo, including a decrease in the number of different microbial species (Ganju 2016).
- Similar results were reported by another study that found different microbial composition in the affected skin of patients with vitiligo (Bzioueche 2020). In this study, researchers found skin affected by vitiligo had reduced levels of Bifidobacterium and elevated levels of Terenicutes, Streptococcus, Mycoplasma.
Warts are a relatively benign condition characterised by small fleshy bumps that can appear in different parts of the skin, including the hands, face, elbows, feet, knees, sole of the feet or elsewhere in your body. Broadly, warts are classified as
- Common warts – affecting hands, elbows and knees
- Plane warts – affecting hands and face, commonly affecting children
- Plantar warts – usually found in the sole of the feet, but can also be present in the heels and toes.
- Filiform warts – these are long and thin warts that can appear on eyelids, armpits or neck.
- Mosaic warts – these are warts that grow in clusters, usually on hands and feet.
DRIVING FACTORS
Warts are caused by infection by the human papillomavirus (HPV). Warts can be contagious, and can be acquired, for example by walking bare feet on a surface containing the virus or through contact with an infected person. Recent studies suggest that a person’s propensity at acquiring HPV and developing warts may be influenced by specific skin features. For example,
- People with compromised immune systems are at increase risk of acquiring an HPV infection (Sri 2012)
- One study found that a patient suffering from skin warts had significantly reduced diversity of viral skin microbiota. In this patient, the viral community was dominate by the HPV (Landini 2015). This observation suggests that skin microbial dysbiosis, particularly within the community of virus normally present on the skin, may have a role with HPV infection and wart development.
SKIN MICROBIOTA AND IMMUNITY
The skin holds a wide range of different immune cells, such as keratinocytes, macrophages, dendritic cells, innate lymphocytes, and different types of T-cells that are involved with innate and adaptive immunity. Some of these cells also produce antimicrobial compounds and specialised molecules called receptors which can sense and respond to the presence of microbes.
Some skin microbes, like Staphylococcus epidermidis have a wide range of functions, influencing wound repair, inflammation, infections and even cancer. Within the context of inflammation, S. epidermidis is known to engage with components of the adaptive immune system, including different subsets of T cells. These immune cells are responsible for the identification of specific targets and leading an immune response aimed at eliminating a target pathogen. S. epidermidis can influence and fine tune these immune responses, effecting affecting our immune response to pathogens.
People suffering from immune dysfunction have been shown to host an altered skin microbiota. For example, a recent study evaluated the bacterial and fungal skin microbiomes of patients suffering from primary immunodeficiency (PID) (Oh 2013). Compared to healthy controls, PID patients shows abnormally high levels of certain bacterial groups, like Clostridium species and Serratia marcescens. Likewise, PID patients had elevated fungal diversity and increased levels of opportunistic fungi, like Candida and Aspergillus.
The gut to skin axis
Both our gut and skin are covered in microbes, all playing important roles affecting our health, as they are important components of the human microbiome. Recent studies have now identified a link between these two microbial populations, hinting at the existence of a communication pathway between the microbes of the skin and those of the gut.
- The gut microbiota (also known as gut microbiome) produces vast amount of chemicals, known as microbial metabolites, which influence difference aspects of our health. While most of these chemicals affect their local environment, some chemicals may pass the intestinal barrier and reach other parts of the body, like the skin.
- For example, free phenol and p-cresol are metabolites produced by gut bacteria, notably by Clostridium difficile (Dawson 2011). One study showed that these two metabolites can reach the circulatory system and accumulate in the skin of mice.
- Other studies have found evidence that p-cresol and phenol in the skin can reduce the expression of certain genes found in keratinocytes, the main skin cell in the epidermis (Miyazaki 2014). Alterations in the function of these cells can lead to deficient epidermal differentiation and epidermal barrier function.
- Beyond metabolites, gut bacteria could also escape the gut and enter the bloodstream, potentially reaching the skin. One study found evidence supporting this scenario, by showing that DNA from gut bacteria can be found in the blood of patients with psoriasis (Ramırez-Bosca 2015).
- From an immune perspective, various studies suggest that intestinal dysbiosis is linked to inflammatory skin diseases. For example, children with reduced intestinal diversity early in life (1 week to 18 months of age) are more likely to develop atopic skin diseases (Elazab 2013, Nylund 2015, Song 2016, Wang 2008, Bisgaard 2011).
- Other studies have reported that allergic children shown gut dysbiosis, particularly after an allergic event (Gore 2008, Sepp 2005, Mah 2006).
FUNCTIONAL MEDICINE AUSTRALIA AND SKIN HEALTH
At the Australian Centre for Functional Medicine we take a comprehensive look at all factors influencing skin health. We employ a Modern approach to Functional Medicine Australia, merging standard medical practices with cutting edge, research-backed approaches, and extensive diagnostic testing.
Skin health is an important aspect of your overall health and it depends on a delicate balance of multiple factors, including the optimal composition of your gut microbiome as well as the skin microbiome. At the Australian Centre for Functional Medicine we follow a constantly updated practice, based on current research findings. Our goal is to understand the underlying factors affecting your skin health and apply the best research-backed treatments to restore your skin and overall health.
Our modern approach to Functional Medicine Australia offers an effective alternative to the standard model of clinical practice. The Australian Centre for Functional Medicine employs leading clinical testing approaches, evaluating biomarkers found in your blood, stool, urine, and breath. Genomic-based tests, for example, are used to inform us about genetic susceptibilities, mutational defects or other factors that may influence treatment efficacy and health. We also test the composition of your gut microbiome, to identify any instances of dysbiosis.
Our comprehensive testing is used to obtain a solid understanding of your physical health, and to garner evidence of any malfunctions potentially affecting your health.
on your path towards healthy skin, and a healthier life.
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