Mary, a 36 year-old hairdresser, has gradually developed itchy redness and some scaling of her hands over the past few months.  Judy, a 21-year-old college student, has developed an itchy red skin rash on her ear lobe since she wore a new nickel earring several weeks ago.  Are both skin conditions the same? contact dermatitis is an inflammation of skin and is due to a chemically induced irritation or an allergic sensitization.  Symptoms may include itching, redness, swelling, blistering, and, in a more chronic form, scaling and even thickening of the skin.  In general, the most severe reaction occurs at the contact site.

Irritant contact dermatitis is triggered by exposure to chemicals such as soaps, detergents, solvents, or cutting agents that are irritating to skin.  Irritant contact dermatitis may affect anyone who has sufficient exposure to irritants.  This condition occurs frequently in health care workers, homemakers, janitors, mechanics, and hairdressers.   Allergic contact dermatitis may look similar to, but is notably different from irritant contact dermatitis.  Allergic contact dermatitis is a hypersensitivity reaction that takes place in people with a genetic predisposition to this condition.  Reactions occur after even brief contact with tiny quantities of allergens.  The initiation of the sensitization process and establishment of immunologic memory usually takes 8-14 days.  Later contact with the same allergen produces inflammation within 6-12 hours and reaches a peak between 48 and 72 hours.

One of the most common allergens responsible for allergic contact dermatitis is a chemical found in poison ivy, oak, and sumac.  Other allergens include nickel and cobalt, found in metal jewelry, clothing snaps, zippers and metal-plated objects; neomycin ointments; potassium dichromate, a tanning agent found in leather shoes and clothing; latex in gloves and rubberized clothing; and certain preservatives, such as formaldehyde.  Both a patient’s clinical history and the distribution pattern of skin eruptions remain essential for physicians to make an accurate diagnosis.  The best way to make a diagnosis of allergic contact dermatitis is to employ patch skin testing, wherein a small amount of the suspected allergen is applied to the skin for a fixed time, usually two days, to determine if a reaction takes place.

The best treatment is to identify and avoid the substance that may have caused contact dermatitis.  Thoroughly wash skin with soap and water as soon after the exposure as possible.  Use wet, cold compresses to soothe and relieve inflammation if blisters are broken.  An antihistamine can help control itching.  For severe inflammation, a corticosteroid can be applied either topically as a cream or ointment, or even orally or as an injection, if necessary.  While irritant contact dermatitis and allergic contact dermatitis may have similar symptoms, they are distinctly different conditions that require unique diagnosis and appropriate treatment.