A rash is characterized by a significant change in the texture or color of your skin. Your skin may become scaly, rough, itchy, or inflamed in various ways. Some rashes are visible even through clothing; others require the use of medical tools to detect them. The most common type of rash is called a dermatitis. It can be caused by something that has been introduced into your body through your mouth or nose (such as food additives or chemicals), but also can be associated with other factors such as atopy (an inherited tendency to develop allergies). Dermatitis can be further divided into two main categories: irritant and allergic. Irritant dermatitis results from exposure to something harsh such as soap or sand. The skin reacts by flaking and becoming red and sore. The person who suffers from this type of rash should avoid further exposure to the cause of the irritation. If you think that you have been exposed to such an irritant, wash your hands well with soap and water immediately following contact with the source of the irritation. Allergic dermatitis results from something inside the body reacting against substances such as pollen or pet dander. These allergens enter through the mucous membranes of the nose or mouth and end up in the skin.