Skin allergies can come in a few different forms, although the term "allergic contact dermatitis" usually refers to itchy, red rashes or bumps that result from an allergen that touches your skin. However, some people refer to other conditions as skin allergies, like the external allergic symptoms of ingested or inhaled allergens and rashes that develop when you touch an irritant.
True allergic contact dermatitis develops when your skin touches something that your immune system identifies as dangerous. The resulting chain reaction of antibodies, mast cells and chemicals like histamine causes a red, itchy, bumpy, blistered and even scaly rash to develop in the spots where you touched the allergen. The rash can appear up to 48 hours after you're exposed to the allergen, and it can take more than a week to go away once you remove the allergen. Hives -- also called urticaria -- most often are the result of an allergen you eat or breathe, but they appear as itchy, red, raised areas on your skin. Contact urticaria can cause hives to appear within a half-hour of when you touch something you're allergic to; a common trigger of this type of skin allergy is latex. However, you can also get hives from touching an irritant that you're not allergic to. Sometimes, hives are accompanied by angioedema, which is the swelling of deep layers of skin. Such swelling doesn't itch or turn red; it normally affects areas like eyelids, lips, hands and feet.
Atopic dermatitis, or eczema, is another condition that affects the skin, and it can be related to allergies. Eczema shows up as a red, scaly, itchy rash, normally on the face, elbows and knees. Most often, allergic eczema is the result of an allergen you ate or breathed in and not of something you touched. However, skin irritants can cause eczema outbreaks.