Introduction:
The skin is the human body's largest organ, acting as a protective barrier and defense against foreign pathogens. The skin is colonized by several microorganisms called microbiome or microbiota. These consist of bacteria, viruses, and fungi. Skin microbiome also strengthens the immune system of the body. The imbalance between the skin microbiome and host immunity can lead to immune-mediated or chronic inflammatory disorders. The imbalance can be due to the external environment, dietary, and lifestyle factors. Due to these factors, there will be regulation of microbial colonization, and these microbes enter the skin, interact with the host cells, such as immune cells, and cause several skin diseases. The article discusses the skin microbiome and its interaction with the immune system.
What Is a Skin Microbiome?
The skin is composed of habitats and microorganisms. The main role of the skin is a physical barrier, meaning to protect the skin from harmful microorganisms. It prevents the penetration of harmful toxins and retains skin moisture and nutrients. The normal process of the skin includes shedding dead cells and forming new skin cells. During this process, several bacteria penetrate the skin. The skin microbiota comprises Staphylococcus, Streptococcus, Actinobacteria, Bacteroidetes, and Proteobacteria. On the skin, the predominant species include Actinobacteria; on the gastrointestinal tract, the predominant species include Bacteroidetes.
Several factors, such as external environment, humidity, and temperature, affect the microbiota distribution. Some skin areas, such as the axilla and groin, are high in temperature. During moist conditions, microorganisms, such as Gram-negative bacteria and Staphylococcus species, inhabit the axilla and groin area. Areas of the body, including the chest, face, and back, are invaded by Propionibacterium species. The normal skin microbiota consists of Staphylococcus aureus, Staphylococcus epidermidis, Propionibacterium acnes, and Corynebacterium diphtheria.
What Is the Role of the Microbiome in Immune System Development?
The microorganisms colonize the skin surface for the immune system's maturation. Immunity plays an important role during the first years of life. There is variability in the microbiota composition before the infant reaches the age of three years. Infants are more susceptible to infections due to environmental exposure, which harms immunity. The immune systems of the infant and newborn are immature and weak, so they are susceptible to harmful infectious pathogens. It is the major cause of death in children. A large amount of microbiota colonized after birth and came from maternal microbiota. Certain factors that impact microbiota colonization include the mode of delivery. The maternal antibodies are delivered to an infant through breast milk. It helps protect an infant against harmful pathogens.
What Is the Interaction Between the Skin Microbiome and the Immune System?
During human development, the composition of skin microbiota changes. In addition, it is also based on age, external environment, and host physiology. The skin microbiota adapts to the person's physiological and immunological skin sites where they inhabit. In addition, the skin microbiota help in immune maturation and influence the function of the sites they occupy. The microbiome remains stable at skin sites for several years.
The skin of infants and adults is the same, but the difference is in their immunity and immune activity. The skin surface of the newborn is colonized by several microorganisms immediately after birth. Microbial colonization is done with maternal and environmental factors. If the microbiome invades the skin during early life, it causes long-term health implications. Infant age is crucial for immune tolerance development. Continued environmental exposure may affect the immune system and modulate cytokines. The human microbiome stabilizes at three years, and then again, microbiome changes occur at the onset of puberty due to hormonal changes. The rise in sebum production occurs at the onset of puberty. With a decrease in sebum production, the normal level of Propionibacteria species also decreases, leading to infections.
What Is the Interaction Between the Immune System and the Gut Microbiota?
The human gastrointestinal tract is constantly exposed to the external environment, such as food and drink. Both harmful and good bacteria live in the gastrointestinal tract. Good bacteria educate the immune system to maintain a healthy and balanced environment. The harmful bacteria affect the normal balance of microbiota and cause disease. Immune receptors and signaling pathways control the immune system and microbiome interaction. Due to the interaction, lymphocytes and inflammatory response will be produced. Some metabolites, such as short-chain fatty acids, regulate immune cells. The microbiome produces short-chain fatty acids through the fermentation of dietary fibers. The intestine absorbs this short-chain fat and then transports it to the circulatory system.
The short-chain fatty acids increase the activity of T cells through the upregulation of gene expression and cell activation pathways and protect the skin barrier function. During an immune response, T cells and macrophages increase. Short-chain fatty acids increase the production of retinoic acid and upregulate the production of regulatory T cells. This will result in a reduction in inflammation, maintenance of the intestinal barrier, and autoimmune diseases.
Microbiome dysbiosis reduces the production of short-chain fatty acids and impacts immune function, such as an alteration in the level of lymphocytes. The alteration in microbial composition may produce harmful inflammatory metabolites and affect the permeability of the intestinal barrier. This can lead to the development of inflammatory bowel disease and autoimmune disease. In type 1 diabetes patients, gut dysbiosis has been recorded. The short-chain fatty acids inhibit histone deacetylases and protect the pancreatic islet cells from inflammatory metabolites. Insufficient short-chain fatty acids may compromise the immune system and make them more susceptible to autoimmune diseases.
How to Support Skin Microbiome and Make People Healthy?
The factors that keep the immune system balanced and healthy are as follows:
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Hygiene and personal care routine by handwashing and disinfectant.
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Maintaining a healthy skin pH. The skin's natural pH is acidic, at 4.1 to 5.8. Lactic, sorbic, and citric acids can maintain this pH. These acids maintain an acidic environment and support a healthy skin microbiome.
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By maintaining a healthy gut. The gut and microbiome are linked to skin health. Healthy foods like fiber, probiotics, and whole foods can maintain gut health.
Conclusion:
Several recent studies have shown that skin microbiota protects the skin against harmful bacteria, fungi, and viruses. The deviation from normal microbiota during childhood may affect the outcome of immune development. Later in life, it may cause various inflammatory and autoimmune diseases. Understanding the role of microbiota in maintaining the immune system is important for human health and is also helpful in developing new therapeutic strategies to maintain the immune system.
