Understanding Post-Injection Inflammation

After any injection, swelling and irritation (inflammation) can occur at the site where the needle entered the skin. This is a reaction to the needle or to the medicine that was injected. Or it may be a reaction to both. The reaction may happen right away. Or it may start hours after the injection. In most cases, the reaction isn't serious and goes away on its own.

What causes post-injection inflammation?

The most common cause is the skin or the immune system's response to the needle or the medicine. Less common causes include an allergic reaction to the medicine. In rare cases, an infection at the injection site can occur.

Symptoms of post-injection inflammation

Symptoms at the injection site may include:

  • Sore when touched

  • Swelling

  • Itching

  • Pain

  • Redness

  • Warmth

  • Rash

Treatment for post-injection inflammation

Treatment depends on the cause and how bad the reaction is. Most post-injection inflammation is mild. It goes away on its own in a few hours or days. If treatment is needed, it may include:

  • Cold packs. These help reduce swelling, itching, and pain.

  • Over-the-counter pain medicines. These help reduce pain and inflammation.

  • Prescription medicine. These treat infection.

Possible complications of post-injection inflammation

Be alert for a reaction all over your body. This may cause symptoms such as a skin rash, severe itching, or raised red bumps called hives. This kind of reaction can be serious, especially if it affects breathing. If you or your child develops symptoms away from the injection site, call your healthcare provider right away for more instructions.

When to call your healthcare provider

Call your healthcare provider right away if you have any of these:

  • Fever of 100.4°F (38°C) or higher, or as directed

  • Severe pain at the injection site

  • Blistering at the injection site

  • Muscle aches

  • Upset stomach (nausea), headache, or dizziness

  • Skin rash, severe itching, vomiting, or hives

  • Symptoms that get worse instead of better

Call 911

Call 911 if any of these occur:

  • Swollen lips, tongue, or throat
  • Trouble breathing