The Role of the Skin Microbiome in Skin Barrier Function

Introduction

The skin is a common part of the human body. It is the outermost part of the body which protects the skin from physical and chemical stimuli. The skin is the main barrier between the human body and the outside environment. The skin is colonized with microorganisms and acts as a barrier to prevent pathogen invasion. The skin microbiome is closely connected with several skin disorders. If there is damage to the skin barrier, the balance between pathogens is disturbed and results in systemic diseases. The article discusses the skin microbiome, the skin barrier, and the role of the skin microbiome in skin barrier function.

What Is a Skin Microbiome?

The skin microbiome is also called skin microbiota and skin microflora. These microorganisms, such as bacteria, viruses, and fungi, are collected within the skin. Microorganisms are present in different areas of the skin, depending on skin texture and thickness. Most of these microorganisms benefit the skin and protect the skin from harmful pathogens. The skin can be dry, moist, or oily. On oily skin, the predominant bacteria include Staphylococci and Propionibacteria species; on moist sites, the prevalent bacteria include Staphylococcus species. There are mixed populations of bacteria on dry skin, but Flavobacteriales and Proteobacteria are most prevalent. Several factors can influence the skin microbiome, such as hormone metabolism, skin pH, aging, childbirth, type of living environment, hygiene, radiation, seasons, and climate. The presence of a skin microbiome is both beneficial and harmful. For example, Staphylococcus aureus colonizes the nostril and protects it from the external environment and harmful bacteria because it is a major cause of serious infection. The benefits of skin microbiome are as follows:

• Fight Against Infection: Some microorganisms protect the skin by making the skin pH acidic, which many microorganisms do not like, and by preventing the invasion of harmful microorganisms.

• Help Immune System Work: The harmful microorganisms alter the immune system. Several microbes in the skin protect the skin and help in the immune system's working procedures. For example, skin protection from harmful ultraviolet rays is the common cause of skin cancer.

What Affects the Skin Microbiome?

Skin microbiota is a group of microorganisms that normally reside in the skin. However, several factors can cause alterations in the microbiome and cause skin problems. The factors that can affect the skin microbiome are as follows:

• Environment.

• Air pollution.

• Exposure to ultraviolet light.

• Genes.

• Smoking.

• Diet.

• Hormonal factors.

• Childbirth.

For example, several hormones release sebum during puberty. Sebum is a natural oil that protects the skin by providing a protective barrier. That is why several teenagers are more likely to develop acne.

What Is the Skin Barrier Function?

The skin is the largest human organ. Its three layers are the dermis, epidermis, and subcutis. The skin's main function is to act as a barrier between microorganisms and the outside environment. It regulates water loss and protects organisms from microbial and chemical factors.

• Epidermis: The superficial layer of the epidermis is stratum corneum. It consists of corneocytes (dried-out cells) and is arranged in a brick-and-mortar pattern.

• Subcutis: This layer of the skin consists of fat cells called adipocytes. It forms an insulating layer that protects the skin and bone from mechanical shocks.

The skin barrier comprises several components: the microbiome, the lipid layer (a fat layer comprising cholesterol and fatty acids that help prevent water loss), and the acid mantle (a combination of sweat and sebum that maintain the skin barrier). The acid mantle acts as a chemical protector due to its acidic nature, making it difficult for the bad bacteria to overgrow. Due to the rise in skin pH, the skin barrier does not provide proper protection against harmful bacteria, and it causes inflammation, causing bacteria to overgrow. The lipid layer prevents water loss from the skin. Any disruption of the lipid layer can cause skin dryness, redness, itching, and flakiness. Harsh soaps and hot water can affect the lipid layer and disrupt skin barrier function.

What Is the Role of Skin Microbiome in Skin Barrier Function?

The common pathogens in the human skin include bacteria, fungi, and viruses. The role of skin microbiome in skin barrier function is described below:

• Role of Skin Microbiome on Immunity: The skin microbiome helps function the immune system and strengthens immunity. The skin microbiome helps the immune system to attack harmful pathogens. T cells are common microorganisms that closely interact with the host immune cells. During the neonatal period, Staphylococcus epidermidis colonizes the skin and establishes immune tolerance by accumulating T cells. In the case of atopic dermatitis (immune-mediated inflammatory disease), the skin is colonized with Staphylococcus aureus. When the stratum corneum layer of the skin has a competent structure with an organized lipid matrix, it prevents Staphylococcus aureus colonization and affects the barrier function.

• Role of Skin Microbiome on Wound Healing: Skin microbiome plays an important role in wound healing. Staphylococcus epidermidis is responsible for reducing inflammation and speeding up wound healing. There is a greater colonization of Staphylococcus and Streptococcus species in people with poorly controlled glucose levels. Staphylococcus aureus is more prevalent in the case of shallow ulcers, whereas in deep ulcers, Proteobacteria species and anaerobic bacteria are more prevalent. During stress or depression, the non-pathogenic microbes transit into pathogenic microbes, affecting the wound-healing process.

• Role of Gut Microbiome in Inflammatory Skin Diseases: Microbiomes are closely connected with skin disorders. The gut microbiome can affect the skin and cause several inflammatory skin diseases, such as atopic dermatitis, acne, and psoriasis (inflammatory skin disease causing itchy rash with scaly patches.

• Skin Microbiome and pH: The important factor maintaining the skin microbiome and skin barrier function is pH. The acidic nature of the skin acts as an antimicrobial activity. Most of the skin surface has an acidic nature with a pH range between 4.1 to 5.8, whereas other parts, such as the anus and toe interdigits, have pH ranges between 6.2 to 7.5. The acidic nature of the skin helps colonize the pathogenic bacteria and acts as a skin barrier. An increase in pH can affect the skin microbiome and make the skin more susceptible to infections. Washing the skin with alkaline soap can facilitate the growth of microorganisms, and using an acidic detergent can help prevent acne formation.

Conclusion

Skin microbes protect the skin from harmful pathogens like bacteria, viruses, and fungi. An imbalance in the skin microbiome may disrupt skin barrier function and cause serious skin infections. People should be educated on how the skin barrier influences skin health and provided with solutions to protect the skin from harmful pathogens so that they can incorporate them into their daily routine. If an individual experiences any change in the skin, they should contact a healthcare professional.