What should I do if my arm swells after receiving an injection?

There are many possible causes of local swelling following an injection. First, the injected medication itself may cause localized swelling. If the drug is known to produce such a reaction, observation alone may be appropriate.

However, if the medication is not typically associated with swelling—as confirmed by consultation with your physician or nurse—and you develop localized swelling after returning home, this warrants caution. It may indicate a secondary infection at the injection site, commonly bacterial in origin. Bacteria may enter the skin through the needle puncture, triggering an inflammatory response characterized by redness, swelling, warmth, and pain.

What should you do in such a case? You should seek an in-person evaluation at a hospital. A physician will assess whether a bacterial infection is present. If fluctuation (a fluid-filled sensation) is detected beneath the area of redness and swelling, an ultrasound examination may be necessary to determine whether an abscess has formed. If an abscess is confirmed, surgical drainage is required; if no abscess is present, topical antimicrobial therapy may suffice.