High Fever: How High Is Too High?

What temperature is a high fever?

Normal body temperature is about 97 °F to 99 °F (36.1 °C to 37.2 °C) and varies through the day. Fever thresholds:

Readings differ by method. Rectal temperatures are the most accurate in babies. Forehead and ear thermometers are convenient but less precise. Mouth readings are about 0.5 to 1 °F (0.3 to 0.6 °C) lower than rectal, and armpit readings lower still.

Is a high fever dangerous?

Fever is the body's defense against infection, and fever from an infection very rarely rises high enough to damage the brain. The brain's thermostat usually keeps it below 106 °F (41.1 °C). The danger lies in the cause (such as meningitis or sepsis) and in complications such as dehydration. Temperatures above 106 °F are more often caused by heatstroke or drug reactions, where the thermostat itself fails, and these are emergencies.

Common causes of high fever

Infections (most cases)

• Viral infections: flu, COVID-19, adenovirus, roseola in toddlers (high fever for 3 days, then a rash), and many others.
• Throat and ear infections: strep throat often causes high fever with a very sore throat and no cough.
• Pneumonia: fever with cough, fast breathing and chest pain.
• Urinary tract and kidney infections: high fever with chills, back pain and burning urination. In young children, fever may be the only sign.
• Skin infections: cellulitis, abscesses.
• Serious infections: meningitis, sepsis, endocarditis.
• Travel-related: malaria, dengue and typhoid after travel to tropical areas.

Non-infectious causes

• Heatstroke: body temperature above 104 °F (40 °C) from heat exposure, with confusion. An emergency.
• Drug reactions: neuroleptic malignant syndrome, serotonin syndrome, malignant hyperthermia, and stimulant overdose.
• Inflammatory conditions: Kawasaki disease, Still's disease, lupus.
• Blood clots, certain cancers such as lymphoma and leukemia, and thyroid storm.

Symptoms that come with a high fever

• chills and shivering as the temperature rises, then sweating as it falls
• headache and muscle aches
• fast heartbeat and breathing
• tiredness, poor appetite and thirst
• mild confusion or vivid dreams, especially in older adults
• febrile seizures in some children aged 6 months to 5 years

High fever in children

Children often run higher fevers than adults with simple viral illnesses. A child with a temperature of 104 °F (40 °C) who is playing and drinking after a dose of fever medicine is usually less worrying than a child with 101 °F (38.3 °C) who is limp and hard to wake.

Febrile seizures happen in about 2% to 5% of young children, usually as the temperature rises quickly. They look frightening but are usually brief and harmless. Lay the child on their side, time it, and call 911 if it lasts more than 5 minutes. Get any first febrile seizure checked.

For age-specific advice, see fever in children and infant fever.

High fever in adults

Adults less often get very high fevers from simple viruses, so a temperature above 103 °F (39.4 °C) deserves more attention, especially with shortness of breath, confusion, a stiff neck, severe pain or a weak immune system. Older adults may have a lower fever, or none, even with serious infections.

When to go to the ER for a fever

Go to the ER or call 911 for any fever with: difficulty breathing, chest pain, confusion, a stiff neck, a non-fading rash, a seizure, severe dehydration, signs of sepsis, a temperature of 105.8 °F (41 °C) or higher, or any fever in a baby under 3 months. See the triage box above for the full list.

How to bring down a high fever

1. Fever medicine: acetaminophen (paracetamol) or ibuprofen, following the label dose for weight or age. Ibuprofen is not for babies under 6 months. Never give aspirin to children or teenagers because of the risk of Reye's syndrome. Do not alternate medicines unless a doctor advises it.
2. Fluids: drink water, oral rehydration solution, broth or diluted juice regularly. Fever increases fluid loss.
3. Light clothing and a comfortable room: remove heavy blankets.
4. Rest.

Avoid cold baths, ice and rubbing alcohol, which cause shivering and can raise core temperature. A lukewarm sponge is optional for comfort.

The goal of fever medicine is comfort, not a normal number. A fever that does not come down fully with medicine is not by itself a sign of a more serious illness.

How doctors find the cause

A doctor will ask about duration, other symptoms, travel, contacts, vaccinations and medical conditions, and examine the throat, ears, chest, abdomen, skin and neck. Tests may include a urine test, blood tests (blood count, CRP, blood cultures), a flu, COVID or strep test, and a chest X-ray. Babies under 3 months usually need a full workup including blood, urine and sometimes spinal fluid tests.

Frequently asked questions

What temperature is considered a high fever?

A high fever is generally 103 °F (39.4 °C) or higher. A fever starts at 100.4 °F (38 °C). Temperatures of 105.8 °F (41 °C) or higher are called hyperpyrexia and need emergency care. In babies under 3 months, any fever of 100.4 °F (38 °C) is an emergency.

How high is too high for a fever in adults?

Adults should seek medical advice for a fever of 103 °F (39.4 °C) or higher, a fever lasting over 3 days, or any fever with confusion, breathing difficulty, chest pain, stiff neck or rash. A temperature of 105.8 °F (41 °C) or more needs emergency care.

Can a high fever cause brain damage?

Fever from infection almost never causes brain damage because the body limits it below about 106 °F (41.1 °C). Brain damage is a risk with extreme temperatures from heatstroke or drug reactions, or from serious infections like meningitis themselves, not the fever.

How can I bring down a high fever quickly?

Take acetaminophen (paracetamol) or ibuprofen at the label dose, drink fluids, wear light clothing and rest in a comfortable room. Do not use cold baths, ice or alcohol rubs. It is normal for the temperature to fall by only 1 to 2 °F rather than to normal.

Should I go to the ER for a 104 °F fever?

Not always. A 104 °F (40 °C) fever in an older child or adult who is drinking, alert and improves after fever medicine can often be managed by phone advice or a same-day appointment. Go to the ER if there are red flags such as confusion, trouble breathing, stiff neck, rash or dehydration.