Allergic reactions are genetically determined, and different substances cause contact dermatitis to develop in different people. A reaction to resin produced by poison ivy, poison oak, or poison sumac is the most common source of symptoms. It is, in fact, the most common allergy in this country, affecting one of every two people in the United States.
Flowers, herbs, and vegetables can also affect the skin of some people. Burns and sunburn increase the risk of dermatitis developing, and chemical irritants that can cause the condition include:
detergents and soaps
glues used on artificial nails
Contact dermatitis can develop when the first contact occurs or after years of use or exposure.
Stasis dermatitis, a consequence of poor circulation, occurs when leg veins can no longer return blood to the heart as efficiently as they once did. When that happens, fluid collects in the lower legs and causes them to swell. Stasis dermatitis can also result in a rash that can break down into sores known as stasis ulcers.
The cause of nummular dermatitis is not known, but it usually occurs in cold weather and is most common in people who have dry skin. Hot weather and stress can aggravate this condition, as can the following:
soaps and detergents
bathing more than once a day
Atopic dermatitis can be caused by allergies, asthma, or stress, and there seems to be a genetic predisposition for atopic conditions. It is sometimes caused by an allergy to nickel in jewelry.
Seborrheic dermatitis (for which there may also be a genetic predisposition) is usually caused by overproduction of the oil glands. In adults it can be associated with diabetes mellitus or gold allergy. In infants and adults it may be caused by a biotin deficiency.
Maureen Haggerty, The Gale Group Inc., Gale, Detroit,