Allergy shots, formally known as Subcutaneous Immunotherapy (SCIT), are a long-term treatment designed to decrease a person’s sensitivity to specific allergens. This process involves regularly injecting small, controlled amounts of substances that trigger allergic reactions, such as pollen or dust mites, into the body. The goal of this therapy is to train the immune system to build tolerance to these triggers, leading to a lasting reduction in allergy symptoms. SCIT is commonly used for environmental allergies, allergic asthma, and insect sting allergies. Treatment often continues for three to five years to ensure long-term effectiveness.
Directly Addressing Post-Shot Fatigue
Yes, allergy shots can cause feelings of fatigue, drowsiness, or general sluggishness in many patients. This is a recognized side effect, though it is usually mild and temporary. The tiredness typically begins a few hours after the injection is administered, as the body starts to process the introduced allergens. For the majority of people, this dip in energy is short-lived and resolves within 24 hours.
In some cases, the feeling of weariness may persist for up to 48 hours, which can be an important factor for patients to consider when scheduling their appointments. Post-shot fatigue is often described as a sense of heaviness, or having a harder time focusing and staying alert. Since the body is actively reacting to the treatment, the immune system’s adjustment period can temporarily drain energy. This common reaction is a normal physiological response to the immunotherapy process.
The Immune Mechanism Behind Tiredness
The underlying reason for post-shot fatigue is the systemic activation of the immune system by the injected allergens. Allergy shots work by repeatedly challenging the body with small doses of an allergen to shift the immune response toward tolerance. This process requires the immune system to work actively, consuming energy that can lead to exhaustion. The introduction of the allergen triggers a complex cascade involving various immune cells and signaling molecules.
Specifically, the immune system releases inflammatory chemicals known as cytokines in response to the injected allergen. Cytokines are small proteins that act as messengers between cells. Certain types, such as interleukins, are known to induce systemic effects like fever, malaise, and fatigue. These chemicals signal the body to rest and conserve energy, a common response when the immune system is actively engaged. The initial immune activity can produce temporary, flu-like symptoms, which are a byproduct of the body successfully re-programming its allergic memory.
Recognizing and Managing Side Effects
While fatigue is common and generally not a concern, it is important to distinguish it from other, more acute reactions to the shot. The most frequent side effects are local reactions, which involve swelling, redness, and itching at the injection site. These localized symptoms usually appear within a few hours and clear up shortly afterward. If an unusually large local reaction occurs, an ice pack or oral antihistamine may be used for relief.
A less common but more serious concern is a systemic reaction, which affects the entire body rather than just the injection site. Mild systemic reactions may include sneezing, nasal congestion, or hives, but severe reactions, known as anaphylaxis, are rare. Symptoms of anaphylaxis can involve a tight feeling in the chest, wheezing, difficulty breathing, or dizziness, which require immediate medical attention. Patients are typically monitored for 20 to 30 minutes after each injection to ensure any immediate, severe reactions are quickly treated.
For managing common fatigue and sluggishness, simple self-care measures are recommended. Patients should prioritize hydration and ensure they get adequate rest following their appointment. Avoiding strenuous exercise for two hours after receiving the injection is also advised, as physical activity can increase the risk of a systemic reaction. If the fatigue is severe, lasts longer than two days, or is accompanied by other concerning symptoms, a patient should consult with their allergist.