when an allergen invades or irritates your body it causes your body to unleash chemicals known as histamines. some people react to a high histamine level by developing the rash we call hives. common allergens that can provoke hives include certain milk products fish and nuts; drugs such as penicillin and aspirin; and various food additives emulsifiers flavorings and preservatives. extreme cold or heat stress and pressure on the skin may induce an attack of hives as can insect bites infections such as strep throat in children and hepatitis b in adults and -- in very rare cases -- blood transfusions.
what causes hives?