Human sensitivity to tartrazine has been reported with some frequency and has been estimated to occur in 1/100000 persons. Anaphylactic, potentially life-threatening, has been reported but symptoms more commonly cited are urticarial (hives), asthma, and purpura (blue or purple spots on the skin or mucous membrane). Of 97 persons with allergic symptoms in one trial, 32 had adverse reactions to challenge with 50 mg tartrazine. Physicians use 0.1-10 mg tartrazine to test for its sensitivity.