Do Allergies Cause a Fever? What Your Temperature Can Reveal

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Do Allergies Cause a Fever? What Your Temperature Can Reveal

By Your Health Magazine Health Information Team

You wake up sneezing, congested and exhausted. Your eyes itch, your throat feels irritated and your face seems unusually warm. When the thermometer shows a higher-than-usual reading, you may wonder: Do allergies cause a fever, or are you coming down with something else?

The short answer is that common environmental allergies, including seasonal allergic rhinitis or “hay fever,” do not typically cause a true fever. A measured fever is more likely to point to an infection, another medical condition or, less commonly, a reaction to a medication. Because allergies and respiratory infections share several symptoms, your temperature can provide a useful clue about what may be happening.

Do Allergies Cause a Fever?

Seasonal and indoor allergies occur when the immune system overreacts to normally harmless substances such as pollen, mold spores, dust mites or pet dander. This response releases histamine and other chemicals that can inflame the eyes, nose, throat and airways.

Typical allergy symptoms include:

• Sneezing
• A runny or stuffy nose
• Itchy, red or watery eyes
• Itching in the nose, mouth or throat
• Postnasal drip
• Coughing related to drainage
• Fatigue, often made worse by disrupted sleep

Fever is not a typical symptom on that list. Despite its name, hay fever does not usually raise body temperature. People who search “does allergies give you a fever?” may be noticing warmth, flushing, fatigue or chills that feel feverish. However, feeling warm is not the same as having a measured fever.

There is an important exception: certain allergic or hypersensitivity reactions to medications can include fever, often along with a rash, swelling or other symptoms. A new fever after starting a medicine should be discussed promptly with the prescribing healthcare professional rather than assumed to be a seasonal allergy.

What Counts as a Fever?

Body temperature naturally varies among individuals and can change with the time of day, physical activity, menstrual cycle, environment and measurement method. Although 98.6°F, or 37°C, is often described as “normal,” healthy temperatures may be somewhat lower or higher.

A reading of 100.4°F, or 38°C, or above is commonly treated as a meaningful fever threshold. Oral, forehead, ear, rectal and underarm measurements are not perfectly interchangeable, so record both the temperature and how it was taken. If you are comparing readings in different units, this guide to understanding body temperature and converting Celsius to Fahrenheit can help put the number in context.

Use a digital thermometer according to its instructions. Touching someone’s forehead may suggest that the person feels warm, but it cannot reliably confirm or rule out a fever.

If It Is Not Allergies, What Could Be Causing the Fever?

When congestion or sneezing occurs with a fever, consider the possibility that an infection is causing the symptoms or occurring at the same time as an allergy flare.

A Cold or Other Viral Infection

Colds can cause congestion, sneezing, coughing and a runny nose, making them easy to confuse with allergies. A sore throat, mild body aches, general illness and a low-grade fever are more suggestive of a viral infection. Influenza and COVID-19 can also cause fever, cough, fatigue, headache or body aches, although symptoms vary from person to person.

A Sinus Infection

Allergy-related swelling can interfere with normal sinus drainage. Viruses are responsible for many acute sinus infections, while some cases are bacterial. Possible symptoms include facial pressure, reduced sense of smell, congestion, headache, cough and thick nasal drainage. Fever can occur, particularly with an acute infection.

The color of mucus alone cannot determine whether an infection is bacterial. Even an ordinary viral cold can produce yellow or green mucus. Symptoms that persist, worsen after initially improving or cause significant facial pain deserve medical evaluation.

An Ear or Throat Infection

Ear infections and infections affecting the throat can occur with nasal symptoms and fever, especially in children. Ear pain, difficulty swallowing, swollen neck glands or a severe sore throat are reasons to contact a primary care professional or pediatrician.

Allergy or Infection? Look at the Pattern

No single symptom provides a diagnosis, but the overall pattern may help you decide whether an evaluation is appropriate.

• Itching strongly favors allergies. Itchy eyes, nose and throat are much more characteristic of an allergic response than a respiratory infection.
• Fever favors an infection. Seasonal allergies should not produce a temperature of 100.4°F, or 38°C, or higher.
• Body aches and chills are more consistent with infection than with uncomplicated allergies.
• Symptoms beginning soon after exposure to pollen, pets, dust or mold may suggest allergies.
• Allergy symptoms may continue for weeks or recur during a particular season, while many uncomplicated viral illnesses improve over several days.
• A severe sore throat, significant breathing difficulty or rapidly worsening illness is not typical of ordinary seasonal allergies.

Allergies and infections can also happen together. A person with spring pollen allergies can still catch a cold, flu or another respiratory infection. Do not dismiss a new fever simply because sneezing and congestion are familiar seasonal symptoms.

What to Do When Allergy Symptoms Occur Without Fever

If your symptoms follow a familiar allergy pattern and you do not have a fever, reducing exposure to the suspected trigger may help. Depending on the allergen, practical steps may include closing windows during high-pollen periods, changing clothes after outdoor activity, showering before bed or limiting exposure to animals that trigger symptoms.

Saline nasal rinses, antihistamines and corticosteroid nasal sprays are commonly used for allergic rhinitis. Use medicines according to their labels and ask a pharmacist or healthcare professional about possible side effects or interactions. Nasal rinsing should be performed only with distilled, sterile or properly boiled and cooled water. For a broader overview of symptoms, testing and treatment, review this MedlinePlus guide to allergies.

If symptoms are frequent, interfere with sleep or work, trigger wheezing, or do not improve with appropriate nonprescription care, a primary care professional or allergist can help identify triggers and discuss treatment options.

When to Seek Care

Contact a healthcare professional if a fever accompanies symptoms you believed were allergies, particularly when the fever lasts more than a few days, reaches 103°F or 39.4°C in an adult, returns after improving, or occurs with worsening cough, severe sinus pain, ear pain, dehydration or unusual fatigue. A primary care professional can evaluate common infections, while an allergist may help with persistent or unclear allergy symptoms.

A baby younger than 3 months with a rectal temperature of 100.4°F, or 38°C, or higher needs prompt medical evaluation, even if the baby otherwise appears well. Parents and caregivers should contact a pediatrician about fever concerns in older infants and children as well.

Seek emergency care for trouble breathing, chest pain, confusion, a seizure, a stiff neck, blue or gray lips, inability to stay awake or signs of a severe allergic reaction. Sudden throat or tongue swelling, widespread hives, faintness or breathing difficulty after exposure to a food, medicine or insect sting may indicate anaphylaxis and requires immediate emergency assistance.

The Bottom Line

Common seasonal and indoor allergies do not normally cause a true fever. If your thermometer reads 100.4°F, or 38°C, or higher, look beyond pollen or pet dander and consider that an infection or another condition may be responsible. Paying attention to itching, body aches, symptom timing and the measured temperature can help you describe the problem clearly and choose the right level of care.