Dr. Bill's Science Information Site.

ARTIFICIAL COLORS IN FOODS.                                                                               
TARTRAZINE (yellow number 5) causes an allergic reaction in susceptible people. Symptoms include hives, itching, and nasal congestion, sometimes severe enough to require medical treatment.  It is not a common problem; only 1 or 2 in 10,000 people may have the reaction.  Still, that is over 20,000 people in the nation as a whole.  People with allergy who react to tartrazine rightly demand to know where the dye is in foods so that they can avoid it.  They cannot just avoid yellow-colored foods, because tartrazine is used to confer turquoise, green, and maroon colors on foods and drugs as well. Legislation is now in force requiring that tartrazine be lised on all labels of foods that contain it so that consumers can avoid it if they wish.