It is normal to get a bump under the skin after getting a shot, explains HealthTap contributor Dr. Nandini Yadav. The bump is a an indication that the body is responding to the injected substance and developing an immune response, notes Dr. Holly Maes.
The swelling typically dissipates within 10 days of receiving the injection, explains Dr. Yadav. Applying warm compresses and moving the arm helps to alleviate symptoms.
A hard lump at the site of an injection may indicate a small accumulation of blood under the skin due to a broken blood vessel, states Dr. Jane van Dis on HealthTap. Such bumps normally resolve on their own; over-the-counter pain relievers can help relieve any discomfort.