Hay fever, or allergic rhinitis, affects millions of people each year, causing symptoms that mimic a cold. Many people wonder whether hay fever can also cause a fever, which is typically associated with an infection. Pure hay fever does not cause a temperature elevation, but the confusion is understandable since both conditions involve the upper respiratory system. Separating the symptoms of an allergic reaction from those of a true infection is important for finding the right relief.
The Typical Symptoms of Hay Fever
Hay fever is an immune system overreaction to harmless airborne particles, such as pollen, mold spores, or pet dander. When the body encounters these allergens, it wrongly identifies them as a threat and launches a defensive response. This resulting inflammation causes a specific set of symptoms.
The classic signs include repeated sneezing, clear and watery nasal discharge, and significant nasal congestion. Individuals also experience intense itching, particularly in the nose, mouth, throat, and eyes. The irritation often leads to red, watery eyes and a persistent cough caused by post-nasal drip.
Why Allergies Do Not Cause Fever
The reason hay fever does not cause a fever lies in the fundamental difference between an allergic response and an infectious response. An allergic reaction begins when the immune system produces Immunoglobulin E (IgE) antibodies in response to an allergen. These IgE antibodies attach to mast cells, which then release inflammatory chemicals, most notably histamine. This release causes localized inflammation, irritation, and the classic allergy symptoms.
Fever, however, is a systemic response involving the entire body. It is triggered when the immune system releases substances called pyrogens in response to a bacterial or viral pathogen. Pyrogens travel to the hypothalamus in the brain, signaling it to raise the body’s core temperature. Since an allergic reaction is a localized response to a non-infectious substance, it does not involve the systemic release of these pyrogens, and therefore, does not induce a true fever.
Common Causes of Fever During Allergy Season
If a person experiencing hay fever symptoms also develops a fever, it indicates that a co-occurring or secondary illness is present. The most frequent culprits are common viral infections, such as the common cold, influenza, or COVID-19, which share many upper respiratory symptoms with allergies. These viral infections are inflammatory responses to a pathogen and cause the body to release pyrogens, resulting in a temperature elevation.
Another common scenario is the development of a secondary bacterial infection, such as acute bacterial sinusitis. Hay fever causes swelling in the nasal passages and sinuses, which prevents normal mucus drainage. This congestion creates an environment where bacteria can multiply, leading to a sinus infection. The resulting bacterial infection, not the allergy itself, then triggers the systemic immune response that includes a fever, often accompanied by thick, discolored nasal discharge.
In these cases, the allergy acts as a predisposing factor by creating conditions for an infection to take hold. The initial allergic inflammation compromises the natural defenses of the respiratory tract, making it more susceptible to pathogens. While allergies do not directly cause fever, they can indirectly lead to complications that do.
Differentiating Symptoms and When to See a Doctor
Differentiating between simple allergies and an infection relies on identifying a few key symptoms. Allergies almost always involve intense itchiness of the eyes, nose, or throat, which is rarely a feature of a cold or flu. Furthermore, the nasal discharge in an uncomplicated allergic reaction is typically thin and clear, whereas a bacterial infection often results in thick, yellow or green mucus.
The presence of a fever, defined as a temperature of 100.4°F (38°C) or higher, strongly suggests an infection is at play. Infections also commonly bring about symptoms like body aches, chills, and profound fatigue, which are generally absent in pure hay fever.
You should seek medical attention if a fever lasts for more than 48 to 72 hours, if you experience a high fever above 102°F, or if you have severe facial pain or pressure suggesting a sinus infection. Difficulty breathing or shortness of breath should also prompt an immediate consultation with a healthcare provider.