Contact dermatitis, commonly referred to as a rash, is a skin reactions to allergy-causing substances (allergens). Contact with or exposure to allergens may cause an itchy rash, as well as redness, swelling, blistering, oozing, crusting, or flaking. Rashes may develop two to three days after exposure to an allergen. Common allergens that cause skin rashes include metals, rubber, hair dye chemicals, clothing dye chemicals, topical antibiotics, skin or hair care products, and poison ivy or other plants. Rashes typically respond to steroid creams and/or oral antihistamines; however, the best method for prevention of rashes is to identify and avoid the allergen trigger.
Hives, or urticaria, are pink welts or swellings that can itch, burn, or sting. Hives can be as small as a pen tip or as large as a dinner plate and can join to form even larger swellings. Hives often disappear within a few hours, though some may last for days or recur continuously over months or years. Hives are typically the result of an allergic reaction, typically to food or medication; however, some causes of hives are non-allergic (infections, sunlight, heat, cold, water, pressure, or exercise) and may be difficult to identify. Hives are typically treated with over-the-counter antihistamines or corticosteroids.
Patch testing is a simple procedure used to help diagnose a skin allergy rash called allergic contact dermatitis. This testing is used to identify if there are specific substances that are causing skin rashes. Several office visits are required for this type of allergy testing. Panels containing small amounts of substances to be tested are placed on your back, and you will need to wear them for 2 days. Additional tape may be applied to the panel to keep it secure. You may not get your back wet during the testing period, including showering. After 48 hours, the panels will be removed from your skin. Two days after the panels are removed you will return to the office again to evaluate your skin's reaction to the substances tested. Your patch testing results will be discussed at your final office visit.