Just Skin Deep — Your Immune System at the Surface
The skin is the human body’s largest organ. At 1.8 square meters for the average adult, skin covers about as much area as a large closet, and accounts for 12-15% of total body weight. The incredible variation in skin — oily, moist, or dry, exposed to light and cold, or dark and warm — even on an individual, creates unique habitats for the thousands of bacterial and fungal species (called commensal microbiota) that live on our skin. The skin immune system may control skin microbes, but our skin commensals can also educate our immune system. How our skin orchestrates this dialogue with microorganisms and physical insult is integral to its function, and to our health.
The skin is an immunologic organ. There are an estimated 20 billion T cells in human skin
— far greater than the number of T cells in the blood — suggesting that
immune defense in the skin is a high priority. The interaction among
skin microorganisms and the immune system is likely not
adversarial most of the time. Interestingly, the incidence of
inflammatory skin conditions like atopic dermatitis in children has
about doubled in the last thirty years, in parallel with the decreased exposure to microorganisms in early life.
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