Hay fever, known medically as allergic rhinitis, is a common condition that affects millions of people, causing symptoms similar to a cold. The core question is whether this seasonal or perennial allergy can cause a true fever. Hay fever itself does not cause a measurable fever. Understanding the difference between an allergic reaction and an infection that triggers a fever is important.
The Mechanism of Allergic Rhinitis
Allergic rhinitis occurs when the immune system overreacts to harmless airborne substances, identifying them as threats. These allergens frequently include pollens, pet dander, mold spores, and dust mites. Upon contact, the body generates specific antibodies, known as immunoglobulin E (IgE).
These IgE antibodies bind to mast cells found in the mucous membranes of the nose, eyes, and throat. Re-exposure to the allergen triggers the mast cells to release inflammatory chemicals, most notably histamine. Histamine is responsible for the familiar symptoms of hay fever, such as sneezing, a runny or stuffy nose, and itchy, watery eyes.
This immune response is highly localized, meaning the inflammation and irritation are confined primarily to the upper respiratory tract. The resulting symptoms are a direct result of this localized chemical release.
Why Hay Fever Does Not Cause True Fever
A true fever, or pyrexia, is defined as a measured elevation of the core body temperature to 100.4°F (38°C) or higher. This rise is regulated by the hypothalamus, the body’s thermoregulatory center in the brain. The hypothalamus raises the body’s temperature set-point in response to substances called pyrogens.
Pyrogens are usually released during a systemic infection caused by bacteria or viruses, signaling a widespread threat. The inflammatory response in allergic rhinitis, driven by histamine, does not generate these circulating pyrogens. Therefore, the localized inflammation of an allergy is insufficient to trigger the brain to reset the core temperature.
While a person with hay fever may feel warm, flushed, or experience general malaise and fatigue, this sensation is not a true, measurable fever. This discomfort is related to the inflammatory process. Taking an accurate temperature reading will confirm that the core body temperature remains within the normal range.
When a Fever Accompanies Allergy Symptoms
If an individual experiences typical hay fever symptoms alongside a measured fever, it indicates a separate or secondary medical issue. The most common scenario is the development of a secondary infection. Nasal congestion and inflammation caused by the allergy can block normal sinus drainage, creating an environment favorable for bacteria to grow.
This blockage can lead to bacterial sinusitis or an ear infection, which are systemic infections that cause a fever. The fever is a symptom of the infection, not the allergy itself. Additionally, hay fever symptoms can be mistaken for a viral illness, such as a common cold or the flu, which often cause a fever.
If a person records a temperature of 100.4°F (38°C) or higher while experiencing allergy-like symptoms, they should consult a healthcare professional. This ensures an accurate diagnosis to determine if the issue is a simple allergy, a viral infection, or a secondary bacterial infection.