A rash is a common allergic reaction. Symptoms develop when the immune system mistakes a substance as a harmful invader. The body sends chemicals and white blood cells to the area perceived to be under attack, creating an inflammatory response. This triggers the rash.
Contact Dermatitis
A contact allergy can be caused by an irritating substance that is organic or synthetic, toxic or nontoxic. Touching one of these substances can cause symptoms in one individual but not in another.
The Mayo Clinic reports that allergic symptoms of itching, redness and bumps or hives can be caused by contact with metals, jewelry or products that contain fragrances, such as perfume or deodorants. Ingredients in cosmetics, skin-care products, soaps, detergents, chemicals and cleaning solvents may trigger a reaction. Touching abrasive fabric or plants such as poison ivy, poison oak or stinging nettles can all cause contact dermatitis.
Atopic Dermatitis
Atopic dermatitis is a form of eczema, a skin disease that presents a characteristic itchy rash. Although a flare-up can be triggered by contact with an allergen, other factors, such as stress, can play a part.
Food and Drugs
Some foods and drugs are well known for causing allergic reactions, such as hives. The Cleveland Clinic reports that foods such as shellfish, peanuts, eggs, milk, wheat and corn create allergy problems for people whose bodies have an intolerance. Adverse reactions to drugs such as penicillin and antibiotics are also common.
Insect Venom
Bee, wasp, hornet and ant stings have a toxic venom. For some people, insect venom causes only mild irritation. Others can have a dramatic reaction, which may start with hives. The Mayo Clinic says severe cases of allergic reactions can lead to anaphylaxis, a life-threatening condition.
