A Rash When Taking Antibiotics - Is It Allergy?

     When a child develops a rash on antibiotics it is commonly assumed that the rash is from an allergy to the antibiotic and the parents are told not to give that antibiotic to the child again. However, allergy may not be the reason for the rash.

     Occasionally, the rash may be part of the disease. There are many viral illnesses that give a child a fever for the first few days (see the articles on “Fever”) and then give the child a rash. By that time, the parent’s concern about the fever may have prompted a visit to the doctor and the child may have been started on an antibiotic. Everyone thinks the rash is allergic and the antibiotic is stopped, but the rash was simply a part of the normal viral process.. Another cause of rash on antibiotics is a rash caused by the antibiotic itself. Some antibiotics can cause rash without it being an allergic reaction and if the child were to keep taking the antibiotic, the rash would go away..

     Finally, it is common for a child who has mononucleosis to develop a rash if the child is placed on antibiotics. We are not sure about why this happens, but it is a common reason for children to be mistakenly labeled as allergic to an antibiotic.

     When trying to decide if a rash is from allergy, look for raised, welt-like hives that itch lot and sometimes appear and disappear over different areas of the body. An allergic reaction usually develops shortly after starting the antibiotic – often after the first dose. If the rash develops after days on the antibiotic, is not raised and does not itch the rash is less likely to be from allergy.