Hay fever is an immune system overreaction to harmless substances like pollen, dust mites, or mold spores. Typical symptoms involve localized inflammation, such as sneezing, a runny nose, and itchy, watery eyes. Despite its misleading name, hay fever does not cause a fever and, by extension, does not directly cause chills. Chills are a systemic response, suggesting a broader issue, meaning that if you experience them alongside hay fever symptoms, the cause is likely a separate, non-allergic condition.
The Distinction Between Allergic Reactions and Fevers
An allergic reaction and a fever represent two fundamentally different defense mechanisms. Hay fever is triggered when the immune system mistakenly identifies a substance, such as pollen, as a harmful invader. This misidentification causes the release of chemicals like histamine, leading to localized symptoms like nasal congestion and irritation. These symptoms are inflammatory but are not part of a systemic fight against a true infection.
In contrast, a fever and accompanying chills are a systemic response used to combat an actual pathogen, such as a virus or bacteria. When the body detects an infection, the brain raises the body’s core temperature set-point. Chills are the body’s way of generating heat, primarily through rapid muscle contraction, to reach this new, higher temperature. This makes chills a sign of a systemic illness rather than a localized allergy.
Secondary Infections: The Real Cause of Chills
If you experience chills while dealing with hay fever, it strongly indicates a secondary infection has developed. Hay fever symptoms, particularly nasal congestion and inflammation, create an ideal environment for pathogens to thrive. Excess mucus production and swelling in the nasal passages can block normal drainage pathways. This stagnant fluid can become a breeding ground for bacteria, leading to conditions like acute sinusitis.
Sinusitis, or a sinus infection, is a common complication of prolonged hay fever that causes true systemic symptoms, including fever and chills. The chills result from the immune response to the bacterial or viral infection within the sinuses, not the allergic reaction itself. Inflammation from post-nasal drip can also irritate the throat, occasionally leading to a bacterial infection that may cause a mild fever. Furthermore, a cold or influenza virus, which causes fever and chills, may simply coincide with an allergy flare-up.
Recognizing Warning Signs and Seeking Care
The presence of chills or a fever should prompt you to stop assuming your symptoms are “just allergies” and consider seeking medical advice. Any temperature above 100.4°F is a true fever and a definite warning sign. If your chills or fever persist for more than 48 hours, or if they are accompanied by other concerning symptoms, you should consult a healthcare provider.
Specific red flags require prompt medical attention, including a fever higher than 103°F (39.4°C), chest pain, or difficulty breathing. You should also seek care if you notice discolored or thick nasal discharge, severe head pain, or neck stiffness, as these can indicate a serious infection. While antihistamines treat allergy symptoms, an underlying bacterial infection causing fever and chills may require antibiotics or other specific treatments.