Most people do not have any bad reactions to allergy shots. Sometimes, you may develop swelling, redness or itching at the site of the injection. These mild reactions typically are treated with antihistamines, and your doctor may decide to adjust the dose for the next injection.
On rare occasions, a more severe reaction will occur. In some sensitive people, the allergy shot can cause asthma symptoms, including difficulty breathing, wheezing or coughing. Or, an anaphylactic reaction will cause dizziness, nausea, a swelling of the throat that can prevent breathing or tightness of the chest. These reactions usually can be treated in the office, but occasionally, they may require treatment at a hospital.