Skin allergies obviously affect the skin, but they also cause reactions in other parts of the body, especially the blood. When the body is exposed to an allergen either through contact or through ingestion, white blood cells start to produce antibodies. The antibodies work to destroy anything that is dangerous to the body, including allergens. In skin allergies, the antibody produced is called immunoglobulin E, which causes the production of certain chemicals called mediators. Mediators, especially histamine, activate more white blood cells and cause a reaction in the blood vessels of the skin. This leads to the formation of rashes, hives, or other skin irritations.