From 5% to 10% of children will develop a rash from amoxicillin after taking it, which in most cases, is considered a side effect of amoxicillin and not an allergic rash. But in a small number of cases, the rash will be a sign of an allergic reaction which means the amoxicillin will need to be stopped right away. Signs that a rash that develops while taking amoxicillin is non-allergic and you do not need to be concerned include:

• The rash starts 3 to 10 days from the day amoxicillin was started, although in some cases it can start earlier
• The rash consists of flat red patches on the skin, sometimes these may be slightly raised or accompanied by smaller pale patches (this is described as a maculopapular rash)
• The rash usually starts on the chest, abdomen, and back, and then spreads to the face, arms, and legs
• The rash may get worse before it gets better but typically goes away within 3 days although can last from 1 to 6 days
• This type of rash caused by amoxicillin is not contagious and your child can go back to school so long as they are otherwise well.

Allergic reactions to amoxicillin tend to happen within two hours of the first dose of amoxicillin and are usually itchy and accompanied by breathing and swallowing difficulties.

Should I go to the doctor if I have a skin rash because of amoxicillin?

That depends on what the rash looks like, how long after starting amoxicillin it appears, and if you have any other symptoms apart from the rash. Go to the doctor if your rash:

• Started within hours of taking the first dose of amoxicillin
• Is raised and very itchy or moves around the body from place to place
• Is accompanied by other symptoms such as breathing or swallowing difficulties, or you feel dizzy
• Includes swelling under the skin or in the facial area.

Mononucleosis and amoxicillin

Viral infections, such as mononucleosis (caused by the Epstein-Barr virus or cytomegalovirus), enhance the risk of side effects with antibiotics, including nonallergic rashes. In general, amoxicillin and other antibiotics aren’t recommended for people with mononucleosis.

How do you treat amoxicillin rash?

The rash should go away by itself, so treatment is not usually necessary.

If the rash is nonallergic, then it is better to continue using amoxicillin rather than stopping or changing to a different antibiotic. This is because changing antibiotics may cause other side effects such as diarrhea or vomiting. Stopping amoxicillin may see your child labeled as penicillin allergic which may limit their access to future antibiotic choices.

An allergist can evaluate your child to see if future avoidance of amoxicillin is needed.

In most cases, the amoxicillin rash does not occur again.