It is a common misconception that allergies directly cause a fever. An allergic reaction itself does not elevate the body’s temperature to a fever state. While allergies can trigger uncomfortable symptoms, a true fever often indicates a different underlying process, such as an infection. Understanding the distinctions between allergic responses and other illnesses is helpful for accurate symptom interpretation.
Allergies and Body Temperature
Allergies occur when the immune system overreacts to a harmless substance, known as an allergen, mistaking it for a threat. This reaction primarily involves the release of chemicals like histamine from immune cells such as mast cells. When histamine is released, it causes localized symptoms like sneezing, itching, swelling, and increased mucus production. For example, in allergic rhinitis (hay fever), these mediators lead to itchy, watery eyes, a runny nose, and nasal congestion.
While histamine can influence body temperature regulation in the brain, allergic reactions do not induce the systemic, widespread immune activation that leads to a fever. The body’s response to an allergen is confined to the area of contact or specific systems, rather than triggering a body-wide temperature increase. Therefore, experiencing a fever alongside allergy-like symptoms suggests an additional condition is present.
Common Causes of Fever
A fever is a temporary rise in body temperature, typically 100°F (37.8°C) or higher orally, and is often a sign the immune system is actively fighting an infection. The body’s thermostat, located in the hypothalamus, raises the body’s set point in response to substances called pyrogens. Pyrogens can be external, such as toxins from bacteria or viruses, or internal, released by the body’s own immune cells during an inflammatory response.
This elevated temperature helps create an environment less favorable for the growth of pathogens. Common illnesses that cause fever include viral infections like colds, the flu, or COVID-19, and bacterial infections such as strep throat, ear infections, or sinusitis. Other causes can involve inflammatory conditions, certain medications, or vaccinations.
Distinguishing Allergy Symptoms from Other Illnesses
Differentiating allergy symptoms from those of infections can be challenging, as both can cause a runny nose, sneezing, and fatigue. Allergies cause itchy eyes, ears, nose, or throat, and clear nasal discharge. Allergy symptoms follow a seasonal pattern or occur consistently when exposed to a specific allergen, and do not include a fever or body aches.
In contrast, infections that cause fever, such as colds or the flu, present with body aches, sore throat, and sometimes discolored nasal discharge. A fever is a common symptom of the flu and can occur with a cold. If allergy-like symptoms are accompanied by a fever, body aches, or a sore throat, it could indicate a viral or bacterial infection, or even a secondary infection like sinusitis that developed due to allergy-related congestion. If a fever is present or symptoms worsen, seeking medical attention is important to determine the underlying cause and receive appropriate treatment.