An allergic reaction that causes bumps on the skin is often from allergic contact dermatitis. Direct contact with an allergen causes the area to become inflamed. A systemic allergic reaction can also cause hives on the skin. Consult with your doctor for a proper diagnosis and treatment of the bumps on your skin.


Bumps that occur from an allergic reaction appear as lesions that may ooze, crust or appear scaly. The area is red, tender and sometimes warm to touch. The rash itches and usually appears within 48 hours of exposure to the allergen. The bumps vary in size and usually disappear within 24 hours, but new bumps can occur as quickly as old ones fade.


The first time you’re exposed to a substance or material, the bumps will not appear, but your immune system starts working to produce antibodies to attack the substance in the future. Strong allergens, such as poison ivy, may only take one exposure while other allergens may take several exposures before bumps occur. Some common substances that cause an allergic reaction on the skin are metals, plants, cosmetics, latex, medications and perfumes. If you develop the antibodies that cause an allergic reaction to one of these substances, the allergy is present for life.


If you come in contact with the allergen that triggers your bumps, thoroughly wash the area as soon as possible with mild soap and water. Rinse all suds from your skin and pat the area dry. This may be the only treatment necessary for mild cases. An over-the-counter topical corticosteroid cream reduces inflammation and redness from an allergic reaction. Oral corticosteroids are taken for severe hives from an allergic reaction to reduce inflammation. Antihistamines relieve the itch associated with allergic contact dermatitis. Wet dressings and cold compresses also help relieve itching. Allergic contact dermatitis will usually clear within three weeks.


Avoiding the allergen is the best way to prevent bumps from an allergic reaction. Consult with an allergist to have a skin test completed to determine the allergen. If the allergen is difficult to avoid and your allergy is severe, immunotherapy injections are sometimes administered to reduce the skin’s reaction in the future. Wear protective clothing and gloves when the likelihood of coming in contact with your allergen is high. Apply an iron-on patch over metal fasteners on jeans so the metal does not come in contact with your skin, according to Mayo Clinic's website.