Possibles Causes

Contact dermatitis results from direct contact with one of many irritants or allergens. Common irritants include laundry soap, skin soaps or detergents, and cleaning products. Possible allergens include rubber; metals, such as nickel; jewelry; perfume; cosmetics; weeds, such as poison ivy; and neomycin, a common ingredient in topical antibiotic creams.

• It takes a greater amount of contact with an irritant over a longer time to cause dermatitis than it takes for an allergen. If you're sensitized to an allergen, just brief exposure to a small amount of it can cause dermatitis. Once you develop sensitivity to an allergen, you typically have it for life.

• Neurodermatitis typically develops when something has created an itchy sensation in a specific area of your skin. This irritation may lead you to rub or scratch your skin repeatedly in that area. Common locations include ankles, wrist, outer forearm or arm, and the back of your neck. Neurodermatitis may also be associated with other skin conditions, such as dry skin, eczema or psoriasis. Contact dermatitis caused by allergens doesn't seem to be a factor, though.

• Atopic dermatitis often occurs with allergies and frequently runs in families in which members have asthma or hay fever. It usually begins in infancy and may vary in severity during childhood and adolescence. It tends to become less of a problem in adulthood, unless you're exposed to allergens or irritants in the workplace.