Allergic reactions are often very complex and can be difficult to determine. Therefore, it is always best to leave it up to experts—for instance allergists or dermatologists—who are familiar with “Contact Dermatitis Patch Testing.” There are several types of allergic reactions with many different mechanisms of action. Three of the most common forms are immediate hypersensitivity, delayed hypersensitivity or allergic reactions, and utricaria. Ingredients that can most often cause such sensitivity are fragrances, preservatives, and some chemical sunscreens. Immediate hypersensitivity is exactly what its name implies: the reaction typically occurs within 30 minutes of being exposed to a product or ingredient to which one is allergic. These reactions can often be very severe, producing significant swelling and redness, and potentially causing a person to go into anaphylactic shock and stop breathing. In the event of a severe reaction, medical treatment should be obtained immediately at a nearby hospital emergency room. In reactions not involving difficulty in breathing, clients should see their physician as soon as possible to minimize the length and severity of the reaction. Treatment usually consists of either injectable or oral steroids, as topical treatment with creams or gels is too slow and usually avoided. Delayed hypersensitivity is a reaction that normally occurs within 24 to 96 hours after a person comes in contact with a product or ingredient to which they are allergic. The reactions observed can range from mild to severe redness and swelling, and the skin can be itchy and somewhat uncomfortable. Normally, there is little potential for anaphylactic shock; however, medical treatment should beobtained as soon as possible to avoid the reaction from getting worse and lasting longer than 7 to 10 days. Utricaria relates to breaking out in hives which are raised red, itchy welts on the surface of the skin. While this type of reaction is more commonly reported as a result of excessive stress, certain foods, medicines, and topical skin care products can also be a cause. Most of the time, these reactions relate to histamine circulating in the blood. They occur within 30 to 60 minutes of coming in contact with a product, and normally go away by themselves within several hours (or faster with an oral anti-histamine). There are a several points worth mentioning about the difference between irritation and allergy. First, irritation is normally less severe and shorter in duration. It usually lasts only a few days compared to allergic reactions, which can require immediate medical care and last up to 10 days. Second, irritation is usually confined to the area to which the product was applied. Allergic reactions can spread to areas near the application site, and in cases where histamine is involved, reactions can occur anywhere on the body. Third, the major difference between irritation and allergy is that once an irritation reaction clears, the product can be reintroduced into a skin treatment regime. If there is an allergy to the product, a person will be allergic to it forever and should never use it again.