inflammation of the skin caused by the direct exposure to various environmental agents—mechanical, physical, or chemical.

The irritants that cause dermatitis may be classified as unconditional or conditional. Unconditional irritants are those that can cause dermatitis in anyone (for example, strong acids, alkalis, high and low temperatures). Conditional irritants are those that cause dermatitis only in persons highly sensitive to them (the so-called allergic dermatitides). Dermatitis is considered either acute or chronic, according to the course of the inflammation. Depending on the nature, strength , and duration of exposure to the irritant, acute dermatitides are characterized either only by reddening and swelling of the skin or by the appearance on reddened skin of blisters that burst to form excoriations: less commonly they are characterized by necrosis and the formation of ulcers. These dermatitides are accompanied by a burning sensation, fever , tingling, sometimes pain, and, less commonly, itching. Chronic dermatitides, resulting from prolonged exposure to comparatively weak irritants, are characterized by a dull bluish color, intensified skin markings, and more or less pronounced thickening of the horny layer.

Dermatitides develop mainly at the site exposed to the irritant. When the irritant is removed, the inflammation disappears relatively quickly. Dermatitides are often seen in industry (occupational dermatitides) and sometimes as a result of therapy (for example, salve dermatitis, radiation burns). Among the mechanical causes of dermatitis, prolonged pressure and friction (formation of sores, usually on the feet, because of poorly fitting shoes, or on the palms, from the friction of oars or the unusual pressure of instruments) are of the most practical importance. The physical factors include high and low temperatures (burns, frostbites) and radiation (solar rays, X rays, and radioactive radiation). Dermatitis is most often caused by chemical factors, the number of organic and inorganic chemical compounds that cause dermatitis is large and keeps increasing with the development of industry. Dermatitis results most often from exposure to turpentine, nickel salts, chromium compounds, and dyes (particularly Ursol, which is used to dye fur and sometimes hair). Some pharmacological agents may cause conditional dermatitides in medical personnel and patients (Novocaine, mercury compounds, certain antibiotics). Dermatitis may result from contact with certain plants. Some of the more than 100 of these plants are unconditional irritants (crowfoot, spurge, fraxinella), others (for example, primulas) may be conditional irritants.

Anti-inflammatory agents, in the form of lotions, salves, and pastes, are used in treating dermatitides. In industry, dermatitis can be prevented by eliminating contact between workers and chemical compounds and supplying workers with special protective clothing and individual protective devices, such as shields, masks, aprons, and gloves.