With an allergic reaction, your immune system, which fights infection and disease, reacts to the drug. This reaction can cause symptoms such as rash, fever, and trouble breathing. True drug allergy is not common. Less than 5 to 10 per cent of negative drug reactions are caused by genuine drug allergy
with a skin test, the allergist or nurse administers a small amount of a suspect drug to your skin either with a tiny needle that scratches the skin, an injection or a patch. A positive reaction to a test will cause a red, itchy, raised bump. A positive result suggests you may have a drug allergy.