Skin allergies can appear in the form of hives, swelling, rashes or eczema. They happen when your skin touches a substance that your immune system misidentifies as harmful. Your body then releases a host of chemicals. One of them, histamine, is responsible for the symptoms that appear on your skin. Depending on the type of reaction and its severity, the duration of symptoms can vary from days to weeks.
Hives are the red, itchy bumps that show up due to a food or drug allergy. They normally go away after a few days. However, some cases of chronic hives can last for months or years. Until hives go away, you can relieve symptoms using antihistamines. Meanwhile, allergic contact dermatitis is the rash that results from you touching something you're allergic to. While it may take up to 48 hours for a rash to appear, it will take anywhere from two to four weeks until the rash goes away, regardless of whether you treat it or not.