An allergic reaction is very much less common than irritative reactions. During life, we estimate that approximately 2% will develop an allergic reaction to a cosmetic product. Allergic reactions manifest themselves in skin contact dermatitis. For such a reaction to take place, one must first develop an allergy. On first use of a drug (new cream) will never get an allergic reaction. The body must first develop an allergy. Prolonged use may immune system develop such sensitivity (allergy). This process is called technical term sensitization. Once one is sensitized, even very small amounts of the product provide a dermatitis reaction in the skin. Typical allergic reactions are swelling, scaling and bags changes in the skin.