Feeling unwell is a common experience many people associate with the peak of allergy season. This sensation often includes symptoms that make one feel “feverish,” prompting a question about whether a simple allergic reaction can elevate body temperature. The short answer is that environmental allergies, such as those caused by pollen or pet dander, do not typically cause a true fever. While the discomfort is real, the symptoms of a severe allergy attack can easily mimic the systemic malaise of an infection.
Allergies and the Absence of True Fever
A true fever is an objectively measured elevation of the body’s core temperature, generally defined by healthcare professionals as \(100.4^{\circ}\text{F}\) (\(38^{\circ}\text{C}\)) or higher. This physiological change is triggered by pyrogens, which are fever-inducing substances released during a bacterial or viral infection. Pyrogens signal the brain’s thermoregulatory center, the hypothalamus, to raise the body’s temperature set point.
In contrast, an allergic reaction does not involve the release of these pyrogens or the subsequent resetting of the hypothalamic thermostat. When the body encounters an allergen, the immune response is localized and chemical, not temperature-driven. If an individual experiences a measured fever along with allergy symptoms, the fever is almost always a sign of a co-occurring infection, such as the flu or a secondary sinus infection. The term “hay fever” is actually a misnomer, as it describes a non-febrile allergic rhinitis.
The Inflammatory Mechanism Causing Malaise
The reason a person can feel so unwell during an allergic episode lies in the widespread release of inflammatory chemical mediators. When a mast cell encounters an allergen, it releases histamine, which causes the familiar local symptoms like sneezing and itching. The immune response goes further, however, activating other cells to release pro-inflammatory signaling proteins called cytokines.
These circulating cytokines are capable of causing systemic symptoms. This flood of inflammatory chemicals triggers a reaction known as “sickness behavior” in the body. Although the hypothalamus’s set point remains normal, the immune signaling leads to profound fatigue, generalized body aches, and malaise. These effects are the components of the feverish feeling, even though the thermometer reading is within a normal range.
Key Differences Between Allergy Symptoms and Illness
Telling the difference between an allergy attack and a viral illness centers on a few distinct physical signs. Additionally, the quality of nasal discharge is often a useful clue for differentiation.
Allergies typically produce a thin, clear, and watery nasal discharge, often accompanied by intense itchiness in the eyes, nose, and throat. In comparison, a bacterial or viral infection, such as a cold, tends to result in thicker, sometimes colored, nasal mucus, and itchy eyes are rare. The duration of symptoms is also a key factor, as allergy symptoms frequently persist for weeks or months, following exposure to the environmental trigger. A common cold or flu typically resolves within seven to ten days.
Severe body aches and muscle pain are common symptoms of an influenza infection, but they are seldom reported as a primary symptom of an allergy. Therefore, if a person experiences significant muscle soreness or a persistent, high temperature alongside their respiratory symptoms, they should consider the possibility of a viral or bacterial infection.