Allergen immunotherapy, commonly known as allergy shots, is a long-term treatment involving a series of regular injections containing gradually increasing amounts of specific allergens. The goal is to slowly desensitize the immune system, shifting the reaction from an inflammatory response to one of tolerance. Patients often seek this treatment for chronic allergy issues like allergic asthma, hay fever, or insect sting sensitivity. A common question among individuals considering or undergoing this therapy concerns the potential for fever as a side effect.
Allergy Shots and Systemic Side Effects
Allergy shots introduce small doses of an allergen into the body, prompting immune activation. This can sometimes lead to side effects categorized as either local or systemic reactions. Local reactions are the most common, typically involving redness, swelling, or itching at the injection site on the arm.
Systemic reactions are less frequent, impacting the body beyond the immediate injection area. Fever is considered a systemic side effect, though it is not one of the most common reactions. If it occurs, the fever is generally low-grade, typically remaining below 100.4°F, and is a temporary sign of the immune system’s engagement.
When fever does occur, it may be accompanied by other temporary, flu-like symptoms, such as mild fatigue, headache, or general body aches. These symptoms usually begin within 30 minutes to a few hours following the injection and resolve relatively quickly. The occurrence of these minor systemic symptoms often prompts a review of the allergen dose to ensure patient comfort and safety during the buildup phase of treatment.
Recognizing Warning Signs of a Severe Reaction
It is important to distinguish a mild, low-grade temperature from a fever that signals a severe allergic reaction, known as anaphylaxis. Anaphylaxis is a rare, life-threatening emergency involving multiple body systems. While a high or persistent fever may accompany a severe reaction, it is rarely the only sign and does not solely define anaphylaxis.
The immediate warning signs of a severe reaction that demand immediate medical attention include difficulty breathing, wheezing, or a sensation of the throat closing. Other symptoms are a rapid or weak pulse, a sudden drop in blood pressure, dizziness, or fainting. Widespread hives, generalized itching, or swelling of the face and mouth are also signs of a systemic response.
Severe reactions most often begin very quickly, which is why patients are required to remain in the clinic for at least 30 minutes after receiving their injection. This observation period allows medical staff to monitor for and immediately treat any adverse reactions. If any severe symptoms appear after leaving the clinic, the patient must seek emergency medical care immediately.
Managing Post-Injection Symptoms
For mild, expected symptoms like a low-grade fever, fatigue, or local swelling, patients can manage discomfort at home with simple steps. Over-the-counter pain relievers such as acetaminophen or ibuprofen can be taken to help reduce the fever and alleviate muscle aches. Applying a cold compress to the injection site can help to minimize any localized redness or swelling that may develop.
Patients should avoid strenuous physical activity or taking a hot bath or shower for at least two hours following the injection. These activities increase blood flow, which may cause the allergen to spread more rapidly and increase the reaction severity. Hydration and rest are also helpful for managing temporary systemic side effects.
While most reactions are mild and manageable, patients should contact their prescribing physician if a fever lasts longer than 24 hours or if the local swelling is excessively large and worsening. Any appearance of the severe symptoms mentioned previously, such as breathing difficulty or widespread rash, also warrants an immediate call to emergency services. The safety protocol surrounding allergen immunotherapy allows the treatment to safely and effectively modify the immune response over time.