Identifying a makeup allergy can be tricky. In daily life, plenty of potential allergens can cause a reaction, such as ingredients in skincare or household products. An allergic response to cosmetic products often manifests as red, flaky, and itchy rashes in areas where you have applied makeup. However, skin reactions don't always appear right away. In fact, you may be able to use a product for several days or months before you experience any symptoms. To treat an allergic reaction from makeup, apply a cool compress before using topical creams like hydrocortisone to calm the skin. If you want to find out which ingredients are causing your allergic reaction, visit a dermatologist's office and ask for an allergy patch test. You should also consider using products with the least amount of ingredients if you have sensitive skin.