A serum sickness-like reaction is the body's reaction to a medicine, infection, or very rarely, a vaccine. It can cause symptoms like:

• Rash
• Hives (raised red bumps on the skin)
• Fever
• Joint pain or swelling

A serum sickness-like reaction is treated by stopping any medicine that may have caused it, treating symptoms, and avoiding what caused it (if possible) in the future.

Follow your healthcare provider's instructions for:

• Giving any medicines as prescribed.
• Giving acetaminophen (Tylenol® or a store brand) or ibuprofen (Advil®, Motrin®, or a store brand) for fever or joint pain. Follow the package directions for how much to give and how often.
• When your child should follow up.

General care:

• For itching and discomfort from hives, put a washcloth wet with cool water on your child's skin.
• Let your child rest as needed.
• Be sure your child drinks plenty of liquids.
• Make sure your child's other healthcare providers and school nurse know your child had a serum sickness-like reaction and what to avoid.

Help your child avoid the cause:

• If a certain medicine or vaccine caused the reaction, your child should not get the medicine or vaccine again. Talk to your healthcare provider about other options.
• Help your child prevent infections by:
  • Teaching them to wash their hands well and often with soap and water and scrub for at least 20 seconds. If soap and water are not available, they can use a hand sanitizer with at least 60% alcohol.
  • Helping them avoid people who are sick.

Your child:

• Has new or worsening symptoms.
• Still has symptoms after 2 weeks.
• Feels better, then gets sick again.
• Has numbness or tingling in the body. This could be a sign of a more serious reaction.
• Has pee (urine) that is tea-colored or that has blood in it. This could be a sign of a kidney injury that needs treatment.

What causes a serum sickness-like reaction? The reaction happens when the immune (germ fighting) system sees certain medicines or substances as something that could cause harm. The immune system reacts by releasing chemicals that lead to the symptoms of the serum sickness-like reaction.

How long do symptoms last? If a medicine caused the serum sickness-like reaction, symptoms often stop within a few days of stopping the medicine. If an infection or vaccine caused the reaction, it can take a few weeks for the symptoms to go away.

Why is it called a serum sickness-like reaction? It is similar to a reaction called serum sickness. However, serum sickness is caused by a reaction to antiserum from animals. Antiserum is a medicine that can treat venomous bites, stings, and certain infections.