Allergy shots (allergen immunotherapy) retrain the immune system to tolerate substances that cause allergic reactions. This therapy involves injecting gradually increasing doses of specific allergens to reduce sensitivity over time, offering long-term relief from symptoms caused by triggers like pollen, dust mites, or insect venom. Because the injection introduces the substance a person is allergic to, there is a risk of an allergic response. A required waiting period immediately following the shot is a non-negotiable safety measure, ensuring any immediate adverse effects can be managed by trained medical staff.
The Mandatory Observation Period
The standard observation time after an allergy shot is typically 20 to 30 minutes, with 30 minutes being the most common requirement. This timeframe is established because nearly all severe, life-threatening systemic allergic reactions (anaphylaxis) occur rapidly after the injection. The waiting period ensures the patient remains in a controlled medical environment during this highest-risk window. Clinic personnel monitor for the rapid onset of a reaction before the patient leaves the facility, which is equipped with trained staff and emergency medications, including epinephrine. Leaving the clinic early negates this safety benefit, as a reaction could begin where immediate medical help is unavailable.
Recognizing Immediate Allergic Reactions
The primary purpose of the observation period is to watch for signs of a systemic reaction, which involves symptoms beyond the injection site. Systemic symptoms can include generalized hives, itching distant from the injection area, sneezing, nasal congestion, or throat tightness. While minor local reactions are common and expected, systemic reactions are less frequent but potentially more serious. More severe symptoms indicating a serious reaction include wheezing, shortness of breath, dizziness, or a sudden drop in blood pressure. These signs point toward anaphylaxis, requiring immediate medical intervention and the quick administration of epinephrine, which works to reverse the dangerous effects of the reaction.
Managing Post-Injection Care and Delayed Symptoms
After safely completing the observation period, patients should be aware of potential delayed effects and appropriate self-care. The most common delayed reaction is local, appearing as redness, swelling, or itching at the injection site. These symptoms typically begin a few hours after the shot, can last up to 24 hours, and are usually managed with a cold compress or over-the-counter antihistamines.
Avoiding Strenuous Activity
To prevent complications, patients are advised to avoid strenuous physical activity for at least two hours following the shot. Increased heart rate and blood flow from exercise can accelerate the absorption of the allergen into the bloodstream, which may increase the risk of a reaction. Activities like hot baths or showers are also often restricted for similar reasons.
Delayed Systemic Reactions
Although rare, a systemic reaction can sometimes occur hours after leaving the clinic, occasionally up to 24 hours post-injection. Patients should monitor for symptoms like generalized hives, difficulty breathing, or dizziness. If these delayed systemic symptoms appear, the patient should immediately administer any prescribed emergency epinephrine and seek emergency medical care.