Skin allergies normally show up in the form of a rash or hives. These symptoms are the result of a mistake by your immune system. When you touch something that your body thinks is dangerous, it sets off a chain of reactions in your body. First, your immune system produces an antibody called immunoglobulin E and tells it to get to work. Then the antibody triggers your mast cells to wage war against the "invading" substance. A bunch of chemicals are produced for that purpose. One of them, histamine, is responsible for most allergic symptoms, including those you see on your skin.
Three substances that commonly cause skin allergies are latex, poison ivy and nickel. Poison ivy can cause itchy, red blisters anywhere that it touches you. Latex is more likely to cause hives than a scaly rash. And nickel skin allergies most often result in itchy, red and sometimes bumpy rashes in the spots that it touched your skin.