Human skin bacterial microbiota homeostasis: A delicate balance between health and disease

Abstract

As the largest organ of the body, the skin acts as a barrier to prevent diseases and harbors a variety of beneficial bacteria. Furthermore, the skin bacterial microbiota plays a vital role in health and disease. Disruption of the barrier or an imbalance between symbionts and pathogens can lead to skin disorders or even systemic diseases. In this review, we first provide an overview of research on skin bacterial microbiota and human health, including the composition of skin bacteria in a healthy state, as well as skin bacterial microbiota educating the immune system and preventing the invasion of pathogens. We then discuss the diseases that result from skin microbial dysbiosis, including atopic dermatitis, common acne, chronic wounds, psoriasis, viral transmission, cutaneous lupus, cutaneous lymphoma, and hidradenitis suppurativa. Finally, we highlight the progress that utilizes skin microorganisms for disease therapeutics, such as bacteriotherapy and skin microbiome transplantation. A deeper knowledge of the interaction between human health and disease and the homeostasis of the skin bacterial microbiota will lead to new insights and strategies for exploiting skin bacteria as a novel therapeutic target.

Keywords: homeostasis; human diseases; skin bacterial microbiota; therapeutics.

Figure 1

Skin physiology. In human anatomy, the skin comprises two distinct layers: the epidermis and the dermis. The surface of the skin is characterized by its acidity, abundance of salts, dryness, and aerobic conditions. In contrast, the invaginations that make up the sebaceous glandular units of the hair follicles are comparatively anaerobic and even richer in lipids. The makeup of the skin's microbiome is influenced by the chemical environment of the skin's ecotone.

Figure 2

Skin bacterial microbiota in human health. Skin microbial homeostasis is critical in maintaining human health, especially by educating the immune system and preventing pathogen invasion. The cutaneous microbiome and the bioactive molecules produced by microbes constantly educate the immune system. In addition, commensal skin microbes create the first line of defence against pathogen invasion by forming a microbial barrier, boosting the chemical barrier, and stimulating innate and adaptive immune defenses.

Figure 3

Skin bacterial microbiota in human disease. Skin microbial disorders in humans can lead to various diseases, including atopic dermatitis, common acne, chronic wound infections, psoriasis, viral transmission, systemic lupus erythematosus, hidradenitis suppurativa, and skin cancer.