Chronic dermatitis is a skin inflammation that causes itching and darkening of part of the skin, states DermNet New Zealand Trust. Dermatitis causes a longstanding irritation on the skin. Although there are different forms of dermatitis, all result from the skin reacting to irritants or allergens, advises News-Medical.net..
Problems in the immune system sometimes cause allergic reactions, explains WebMD. Once a person touches something, the immune system mistakenly thinks that the body is being attacked. The immune system, therefore, releases antibodies and chemicals, such as histamine, causing allergic reactions, such as dermatitis. In other cases, when the skin comes in contact with a certain substance, it removes the skin's surface oils. Without the protective oils, dermatitis occurs when the skin becomes irritated.