Allergies are your body's overreaction to certain substances. Skin allergies happen when your skin touches something that your immune system believes is dangerous -- even though it isn't. When your immune system is triggered by an allergen, your white blood cells send out an antibody called immunoglobulin E to combat the allergen. The antibody then sends out mediators, which are chemicals and hormones it hopes will neutralize the unwanted substance. The mediators can affect your skin and tissues, which is why you end up with allergy symptoms when your allergies are triggered.
The symptoms of skin allergies -- also known as allergic contact dermatitis -- often involve redness, itching, pain, swelling and heat. Causes can include contact with dyes, cosmetics, perfume, latex, topical medications, poison ivy, detergent and some metals. You can narrow down what triggers your allergies if you pay attention to when you have a reaction. An allergist can further the diagnosis through skin testing.