No, allergies do not directly cause a fever. Allergies share many symptoms with sinus infections, including runny nose and itchy, watery eyes, but they can’t cause a fever.
In fact, taking your temperature can help your healthcare provider determine whether you’re dealing with allergies or an infection. For adults, a fever is any temperature higher than 100.4°F. For children, a temperature of 99.5°F measured orally, 100.4°F measured rectally, or 99°F measured under the arm is considered a fever.
When you get an infection, such as bronchitis or strep throat, your immune system releases chemicals that increase your body heat and core temperature. You may also get chills, which further increase your body temperature. Then, when your core temperature resets, you start feeling warm, which can make you sweat. Most of us are familiar with this cycle of chills and sweating that accompanies colds, the flu, and other illnesses. Allergy symptoms alone cannot cause this type of reaction in your body.
If airborne allergens like pollen, dust, or pet dander are triggering your symptoms, an air purifier can reduce your exposure, which may ease symptoms.
Key takeaways
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Allergies do not cause a fever. Not seasonal allergies, not hay fever, not food allergies.
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A fever means something else is going on, usually a viral or bacterial infection like sinusitis.
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Allergies can feel feverish, with fatigue, facial pressure and a hot, flushed feeling, without raising your temperature. Take your temperature rather than guessing.
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Fever thresholds: above 100.4°F for adults, and for children 99.5°F orally, 100.4°F rectally, or 99°F under the arm.
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Allergies can indirectly lead to a fever by setting up a sinus infection, which is bacterial or viral and does raise your temperature.
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A fever in a baby under three months old needs same-day medical attention, whatever else is going on.
Allergies don’t cause a fever
An allergic reaction happens when your body’s immune system overreacts to an everyday substance, such as pollen or pet dander. Allergens like these aren’t harmful on their own, but your body’s reaction to them can cause unpleasant symptoms. For pollen or seasonal allergies, symptoms can include
itchy eyes, nose or throat, fatigue, sneezing, and skin irritation. Some people also get wheezing or chest tightness, which means the allergy is affecting the airways and is worth raising with a doctor. Actual swelling of the throat, lips or tongue is not a normal allergy symptom and needs emergency attention, not a wait-and-see approach.
They may make you feel sick and tired, but pollen or seasonal allergies cannot cause a fever or chills. Even hay fever (another term for allergic rhinitis) won’t cause an actual fever, despite its name.
What about cedar fever?
Same answer, same reason. Cedar fever is the common name for the allergic reaction to mountain cedar pollen, which blankets central Texas from December through February. It can leave you exhausted, congested and feeling genuinely unwell, which is why it picked up the name. It is still an allergy, so it does not raise your temperature. If you have a thermometer reading above 100.4°F during cedar season, that is an infection, not the cedar.
Food Allergies
Food allergies can also cause a wide range of symptoms, including hives, stomach cramps, bloating, diarrhea, and vomiting. A severe allergic reaction may even lead to a potentially life-threatening condition called anaphylaxis, which causes symptoms such as throat tightening, difficulty breathing, swelling of the face or tongue, and faintness. That is a medical emergency: use an epinephrine auto-injector if one is available and call emergency services immediately. However, food allergies won’t cause a fever either.
When allergies lead to something that does cause a fever
Allergies cannot raise your temperature, but they can set up the conditions for something that will. Prolonged allergic inflammation swells your nasal passages and blocks sinus drainage, and blocked sinuses are where bacterial or viral sinus infections take hold. That infection can cause a fever, along with facial pain, thick discolored mucus and symptoms that worsen after seeming to improve.
So if you have had allergy symptoms for a while and then develop a fever, the allergies have not changed character. Something else has started, and it is worth having it looked at.
Fever phobia
Fevers and severe illness often go hand-in-hand, but the fever itself is rarely the problem. A fever is your body’s response to inflammation caused by the immune system’s response to infection or autoimmune diseases. When your body temperature rises, it helps your immune cells perform while damaging the pathogens and infected cells your body’s trying to fight.
It is a common misconception that a fever from an ordinary infection will harm the body or cause brain damage, especially in children. Fevers caused by infection do not reach the temperatures at which that could happen. Body temperature only rises above 108°F (42°C) in circumstances like extreme heat exposure, not from an infection alone. What matters is the cause of the fever and how the person seems, rather than the number itself, which is why the guidance below is about symptoms and age rather than degrees.
So, while fever-reducing medications can be used to lower body temperature and make you more comfortable when you’re sick, they won’t treat the cause of the fever or make an infection go away any faster.
When to see a doctor about a fever
Most fevers resolve on their own within a few days and do not need treatment beyond comfort. Some do need attention, and the age of the person matters more than the number on the thermometer.
Seek medical care the same day if:
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A baby under three months old has a rectal temperature of 100.4°F or higher. This is urgent regardless of how well the baby seems.
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A child of any age seems very unwell, is difficult to wake, is not drinking, has no wet diapers, or has a rash that does not fade when pressed.
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A fever lasts more than three days, or comes back after going away.
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There is a stiff neck, severe headache, confusion, difficulty breathing, chest pain or persistent vomiting.
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The person has a weakened immune system or a serious underlying condition.
If you have allergy symptoms and a fever together, the fever is coming from something else. That is worth getting looked at rather than treating as a bad allergy season.
Other causes of fevers
Fevers are usually caused by viral or bacterial infections, and they typically go away within a few days. However, some other conditions can cause elevated body temperature, such as heat exhaustion, autoimmune disease, inflammatory conditions, cancerous tumors, and some medications or immunizations.
Allergy symptoms can be pretty uncomfortable, and they may sometimes feel similar to cold or flu symptoms, but they won’t cause a fever. Your healthcare provider can help you determine what’s causing your fever and whether you need treatment.
FAQs
Can allergies cause chills?
No. Chills are part of the fever process: your body raises its temperature set point, and you feel cold until your actual temperature catches up. Allergies do not trigger that mechanism. If you are getting chills, something else is going on, usually an infection.
Can allergies cause a low-grade fever?
No, not even a low one. Allergic inflammation is localized and does not reset your body’s temperature control. A reading above 100.4°F is a fever regardless of how mild it looks, and it has a cause other than your allergies.
Why do I feel feverish when my allergies flare up?
Because several allergy symptoms mimic the feeling without the temperature. Sinus pressure, fatigue, a hot flushed face, body aches from poor sleep and a blocked nose all feel like the start of an illness. The thermometer is the way to tell them apart, which is why it is one of the first things a clinician will check.
How can I tell allergies from a cold or COVID?
Fever is the clearest single divider, since allergies do not cause one and both colds and COVID can. Allergies also cause itching, particularly of the eyes, nose and throat, which infections generally do not, and they persist for as long as you are exposed to the allergen rather than running a course over a week or two. Body aches and a loss of taste or smell point away from allergies. If you are unsure, test rather than guess.
Can an air purifier help with allergy symptoms?
It can reduce the airborne allergens you are exposed to indoors, which is a different thing from treating the symptoms themselves. It will not do anything about a fever, because allergies were never causing that.
