Can allergies cause fever?

Allergies and fever are both reaction from immune system. While fever is way to battle infections, allergies are overreaction to harmless substances.

Can allergies cause fever?
Viktor Simunović, Viktor Simunović
27 Mar 2024.

Contrary to common misconceptions, allergies do not directly cause fever; they trigger an immune response that can mimic some flu-like symptoms, excluding an elevated body temperature.

Seasonal allergies, often pollen-induced, lead to allergic rhinitis, characterized by symptoms such as sneezing, nasal congestion, and itchy eyes. These symptoms result from the body's release of histamines in response to perceived threats, not from the pyrogenic (fever-causing) substances associated with infections.

However, severe allergic reactions can result in secondary infections like sinusitis, which may induce fever. Additionally, allergic treatments, such as allergy shots, can, in rare instances, cause systemic effects, including fever, as an indirect outcome.

Can allergies cause fever indirectly?

While allergies do not directly cause fever, certain complications from allergic reactions may lead to conditions that can indirectly trigger a fever. For instance, severe allergic reactions to an allergen can sometimes escalate into secondary infections, such as sinusitis or pneumonia, which are known to induce fever.

Specifically, in cases of hay fever, where symptoms include nasal congestion and itchy eyes, persistent inflammation and irritation can compromise the nasal passages. This makes them more susceptible to infections, consequently potentially leading to fever.

Additionally, while allergy shots are an effective method to manage allergies, they occasionally cause local reactions that might rarely escalate, contributing to systemic effects, including fever, which are an indirect consequence of the body's response to the introduced allergen.

Hay fever vs. fever

Contrary to common misconceptions, hay fever, also known as allergic rhinitis, does not involve an actual fever, distinguishing it from true fever conditions caused by infections. This differentiation is vital in the domain of diagnosing and managing patient symptoms.

Hay fever is an allergic response to outdoor or indoor allergens such as pollen, dust mites, or pet dander, leading to inflammation and irritation of the sinus passages. This inflammation can increase mucus production but does not cause a fever.

Allergists emphasize that the body's temperature remains within the normal range in cases of hay fever. The term 'fever' in hay fever is a misnomer and can mislead individuals to erroneously conflate allergic reactions with the body's fever response to infections.

What can cause allergy symptoms and fever?


While allergies themselves do not directly cause fever, they can lead to sinusitis, an inflammation of the sinuses, which is a condition that may manifest both allergy symptoms and fever. Sinusitis often develops as a secondary infection following a viral cold or flu, complicating the body's initial allergic response. In such cases, the congested sinuses fail to drain properly, creating an ideal breeding ground for bacterial pathogens.

This bacterial invasion can exacerbate the inflammation initiated by allergens, leading to symptoms such as nasal congestion, pain, and potentially fever.


Influenza, commonly known as the flu, is a viral infection that affects the respiratory system. Unlike allergies, which are allergic reactions, the flu is triggered by influenza virus strains. The body's immune response to the flu virus can cause symptoms that mimic allergic reactions, such as nasal congestion, sneezing, and sore throat. However, fever is a distinguishing factor, as it is typically absent in allergic responses.

Common cold

The common cold, often mistaken for allergy due to overlapping symptoms such as sneezing and nasal congestion, can also induce fever, differentiating it from typical allergic reactions.

Caused by various viruses, with rhinoviruses being the most common, the cold triggers an immune response leading to the release of pyrogens. These substances act on the hypothalamus, the body's thermostat, to increase body temperature as a defense mechanism. Unlike allergies, which are mediated by IgE antibodies reacting to specific allergens, the common cold's symptomatology, including fever, results from the body's attempt to eradicate viral pathogens.

COVID - 19

In contrast to common colds, COVID-19, a disease caused by the SARS-CoV-2 virus, can present with both symptoms typically associated with allergies, such as cough and shortness of breath, and fever, illustrating the body's systemic response to this novel coronavirus. The presence of fever in COVID-19 differentiates it notably from typical allergic reactions.

Scientific evidence suggests that the fever results from the immune system's attempt to eradicate the virus, indicating a systemic infection rather than a localized allergic response. While allergy symptoms are primarily mediated by histamine release from mast cells, COVID-19 involves a complex immune system interaction with the virus, leading to a broader range of symptoms, including fever, a key indicator of viral infection.


In summary, while allergies do not directly cause fever, they can lead to conditions that may induce fever as a secondary symptom. Allergies may elevate body temperature slightly but do not typically result in a true fever.

Differentiating hay and actual fever is important for accurate diagnosis and treatment. Understanding common allergy symptoms and recognizing when they co-occur with fever can aid in identifying potential underlying infections or complications necessitating medical attention.

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