Skin: A Natural History by Nina G. Jablonski

Author:Nina G. Jablonski [Jablonski, Nina G.]
Language: eng
Format: epub
ISBN: 9780520275898
Publisher: University of California Press
Published: 2013-02-19T13:00:00+00:00

Dermatitis

Human skin is designed to resist all manner of chemical and biological attacks. The skin’s immune system resembles a modern army, with several specialized types of defensive cells and chemicals that are deployed in different arrays and at different times depending on the nature of the attack (figure 31). The skin responds first by immediately producing chemicals that cause inflammation or fight infection. This so-called innate response then triggers an adaptive response, which is initiated by the Langerhans cells of the immune system that are based in the epidermis. When sufficiently stimulated, the Langerhans cells turn into a marauding army that can migrate from the skin to nearby lymph nodes, where they can induce the formation of infection-fighting lymphocytes. Often, this battle against foreign chemicals or pathogens becomes visible and palpable. Our skin gets red and itchy. Sometimes it develops small bumps filled with clear fluid. If the irritation lasts long enough, the skin can become thick and scaly. All of these effects are related to dermatitis.

Simply defined, dermatitis is inflammation of the skin. Because inflammation can result either from an external irritant or from a chemical imbalance within the body, dermatitis encompasses an enormous range of skin diseases.11 The most common types, referred to as contact dermatitis, are caused by contact with a chemical irritant or microorganism. A classic example of contact dermatitis is poison ivy or poison oak. The itching (pruritis) that almost always occurs with dermatitis results from the chemicals the body produces as part of the inflammatory process. These in turn stimulate an itch-specific neuronal pathway. The delightful, though short-lived, relief provided by scratching is apparently related to the mild pain it causes, which inhibits those neurons.12

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