Alternation in the Human Microbiome With Commonly Used Topical Medications

The microorganisms present on human skin influence human health and disease. Older methods of studying the skin microbiota, such as culture based techniques, favored bacteria, which readily grew under standard laboratory conditions, compared to current molecular approaches, which have shown a greater diversity of skin microbiota. Human skin is a large organ that contains a wide range of physiological and topographical diversity. Distinct niches exist which predispose certain areas, such as hairy, moist underarms to a different bacterial community from dry, smooth sites, such as forearms. Given that the skin is a critical barrier between the body's internal environment and the external environment, characterization of the microbiota of the skin may provide insight into the balance between skin health and disease.

Certain inflammatory skin diseases, such as seborrheic dermatitis, atopic dermatitis and psoriasis, have characteristic sites of involvement. The NIH funded Human Microbiome Project (HMP) aims to characterize the human microbiota and its role in health and disease. Recent research by the HMP showed that certain sites, such as the antecubital and popliteal fossa, sites commonly affected in atopic dermatitis, shared similar groups of organisms and distinct microbial communities. Sebaceous sites, commonly affected in seborrheic dermatitis, also shared similar microbial communities. In addition, Kong et al., showed that changes in microbial communities were temporally associated with disease flares in atopic dermatitis patients. Changes in the microbial communities in atopic dermatitis patients were not only associated with disease flares, but were also associated with whether the patient received treatment with topical medications, including antimicrobial or anti-inflammatory medications, during flares. These findings suggest that communities of microbes are important in the initiation and perpetuation of certain skin diseases and that the topical medications used in treatment of these diseases have an important role, which may be related to their alteration of the microbiome.

The most commonly used treatments in dermatology include topical steroids and topical antifungals, which have long established safety and efficacy. Understanding the changes that these topical medications cause in the human microbiome will provide further insight into their role in the treatment of certain skin diseases and may assist us in developing new therapies in the future.