Do Allergies Cause Fever? – Healthnile.com

Many people notice sneezing, congestion, and watery eyes during allergy season and wonder if a fever could be part of the problem. The term “hay fever” makes it sound likely, but the name is misleading. Allergies, including hay fever and allergic rhinitis, do not directly cause a fever.

Allergies can create conditions that make infections more likely. For example, when allergies cause sinus congestion, this may lead to sinusitis, which can bring on a fever. Cold or flu viruses may also overlap with allergy symptoms, making it harder to tell what is really going on. Understanding the difference between allergy symptoms and signs of infection helps prevent confusion and unnecessary worry.

Definition of Symptom

A symptom is a change in the body that a person can notice or feel. It signals that something may be wrong, but it does not explain the exact cause. With allergies, people often experience sneezing, itchy eyes, watery eyes, runny nose, congestion, and coughing.

These signs happen when the body reacts to allergens like pollen, dust, or pet dander. Some symptoms overlap with those seen in infections. For example, a sore throat, fatigue, body aches, or headache can appear in both allergy and flu symptoms. This overlap sometimes makes it difficult to tell the difference between the two.

Unlike infections, allergies usually do not cause a fever. A high fever is more likely linked to a viral or bacterial illness. However, congestion from allergies can sometimes lead to secondary problems, such as sinus infections, which may include fever.

Common Allergy Symptoms	Common Infection Symptoms
Sneezing	High fever
Itchy or watery eyes	Body aches
Runny or stuffy nose	Sore throat
Coughing or wheezing	Fatigue
Skin rash or hives	Vomiting, diarrhea
Nasal discharge	Headache

Some people may also experience swelling, chest congestion, or skin rash during allergic reactions. In more severe cases, hives and itching can occur. Infections often bring vomiting, diarrhea, or a high fever, which are not typical allergy symptoms.

Possible Causes/Diseases Condition

Allergies themselves do not directly cause a fever. However, they can create conditions that make a person more likely to develop an infection, which may then lead to fever. Common conditions linked to fever with allergy-like symptoms include:

Viral infections such as the common cold or influenza.
Bacterial infections like sinusitis or strep throat.
Respiratory illnesses including COVID-19 or bronchitis.

A sinus infection (sinusitis) can develop after prolonged nasal congestion from allergies. When inflammation and trapped mucus occur, bacteria or viruses may grow, leading to fever, headache, and facial pain. The flu (influenza virus) can cause fever, chills, sore throat, and body aches. These symptoms may overlap with seasonal allergies, but the presence of fever usually points toward infection rather than allergy.

The common cold, caused by several viruses, may also bring mild fever, runny nose, and cough. Unlike allergies, colds usually resolve within a week and may include fatigue. COVID-19 and other respiratory infections can mimic allergy symptoms with congestion, cough, or sore throat. Fever, however, is a key sign that infection is present rather than an allergic reaction.

Condition	Likely to Cause Fever	Key Features
Allergies	No	Sneezing, itchy eyes, runny nose
Sinus infection	Yes	Facial pain, congestion, fever
Common cold	Sometimes	Runny nose, cough, mild fever
Influenza	Yes	High fever, body aches, fatigue
COVID-19	Yes	Fever, cough, loss of taste/smell

Other Non-Disease Causes

Fever usually points to an infection, but other non-disease factors can raise body temperature. These causes are not linked to allergens or the immune system directly, yet they may appear alongside allergy symptoms.

Environmental factors can play a role. Spending time in hot weather, exercising intensely, or staying in poorly ventilated spaces may increase body heat. Unlike infections, these situations cause a temporary rise in temperature that improves with rest and hydration.
Dehydration is another common trigger. When the body lacks enough fluids, it struggles to regulate heat. This can make someone feel warm or flushed, even though no illness is present.
Stress and fatigue may also affect temperature. The body responds to stress hormones by speeding up certain processes, which can lead to a mild rise in warmth. Sleep loss can have a similar effect.

Factor	How It Affects Temperature
Hot weather	Raises body heat externally.
Exercise	Increases metabolic activity.
Dehydration	Decreases cooling effectiveness.
Stress/Fatigue	Modifies hormonal reactions.

These causes differ from allergy-related issues. Allergens like pollen, dust mites, pet dander, or mold may irritate the sinuses or airways, but they do not directly create fever. Instead, they can make someone more vulnerable to infections, which are the true source of fever.

How It Causes the Symptom

Allergies rarely raise body temperature. Instead, they trigger an immune system reaction that releases chemicals like histamines. These chemicals cause swelling, itching, and congestion but do not directly signal the body to create a fever.

When congestion blocks the sinuses, trapped mucus can allow bacteria or viruses to grow. This can lead to sinus infections, which may cause a true fever. In this case, the fever comes from the infection, not the allergic reaction itself.

The hypothalamus, the part of the brain that controls temperature, responds to signals from infections. Since histamines and other compounds from allergies do not act as these signals, they do not usually cause the hypothalamus to raise temperature.

Sometimes, prolonged allergic inflammation may make the body feel weak or achy. While this may feel like a fever, the actual body temperature usually remains normal. If someone experiences allergy-like symptoms with fever, it is more likely due to an infection such as the flu, cold, or sinusitis rather than the allergy itself.

Possible Complications

Allergies do not directly cause fever, but they can set the stage for problems that may lead to one. When nasal passages stay swollen and filled with mucus, bacteria or viruses can grow more easily. This may result in sinus or ear infections, which often bring low-grade fevers. Common complications linked to untreated or poorly managed allergies include:

Sinus infection (sinusitis) – facial pressure, thick nasal discharge, and possible fever.
Ear infection – ear pain, fluid buildup, and fever in some cases.
Asthma flare-ups – coughing, wheezing, and breathing trouble.

For people with ongoing symptoms, an allergy specialist may recommend treatments to lower sensitivity to allergens and reduce complications over time. If a fever develops along with allergy-like symptoms, an infection is the more likely cause.

When to Seek Medical Attention

A mild fever with allergy-like symptoms often suggests an infection rather than allergies. If the fever is low and goes away within a day, most people can manage at home. But certain signs mean you should see a doctor. See a doctor if:

Fever reaches 103°F (39.4°C) or higher.
Fever lasts more than 3 days.
Symptoms get worse instead of better.

Some symptoms that need urgent care include:

Symptom	Why It Matters
Difficulty breathing	May signal a severe reaction or infection.
Chest pain	Could point to a heart or lung issue.
Stiff neck	Sometimes linked to serious infection.
Severe headache	Could suggest more than just allergies.
Rash or swelling	Could be part of an allergic reaction.

Even if the fever is not very high, contact a healthcare provider if you have ongoing sinus pain, ear pressure, or thick nasal discharge. These may suggest a sinus infection after allergies. Children, older adults, and people with weak immune systems should be cautious. They may need medical attention sooner, even with milder symptoms.