Fever and Headache Together: Causes and Warning Signs

Why fever causes headache

When you have an infection, your immune system releases chemical messengers (cytokines) that raise your body's thermostat and also make pain nerves around the head and its blood vessels more sensitive. Dehydration from sweating and not drinking enough makes the headache worse. That is why most fevers come with a dull, throbbing, all-over headache that improves as the temperature comes down.

The key question is whether the headache is simply part of a general infection, or whether the infection is in or around the brain itself.

Common causes of fever and headache

Viral infections

• Flu: sudden high fever, headache, severe body aches, chills, cough and exhaustion. Headache is often prominent behind the eyes.
• COVID-19: fever, headache, sore throat, cough, tiredness and sometimes loss of smell or taste.
• Colds and other respiratory viruses: low fever, runny nose and a mild headache.
• Stomach viruses: fever, headache, vomiting and diarrhea.
• Glandular fever (mononucleosis): fever, headache, very sore throat, swollen neck glands and fatigue lasting weeks.

Bacterial infections outside the brain

• Sinusitis: pressure and pain over the forehead, cheeks or between the eyes, worse when bending forward, with a blocked nose and thick discharge.
• Strep throat: sudden sore throat, fever, headache and swollen glands without cough.
• Pneumonia: fever, cough, chest pain and breathlessness, often with headache.
• Urinary or kidney infection: fever, back or side pain and burning urination; headache is common.

Serious causes of headache with fever

Meningitis

Meningitis is inflammation of the membranes around the brain and spinal cord. Bacterial meningitis can become life-threatening within hours. Viral meningitis is more common and milder.

Classic signs:

• severe headache
• fever
• stiff neck
• sensitivity to light
• nausea and vomiting
• confusion or drowsiness
• in meningococcal disease, a rash of tiny red or purple spots that do not fade under pressure

Not everyone has every sign. Babies may only be irritable, floppy, feeding poorly or have a bulging soft spot.

Encephalitis

Encephalitis is inflammation of the brain itself, usually from a virus such as herpes simplex. It causes fever and headache with confusion, personality change, seizures, weakness or speech problems.

Brain abscess

A pocket of infection in the brain, often spreading from the ears, sinuses or teeth, or after a head injury. It causes a worsening headache, fever and sometimes new neurological signs.

Travel and tick-borne infections

• Malaria: fever, chills, sweating and headache coming in cycles, after travel to sub-Saharan Africa, South Asia or other malaria regions. It can be fatal and needs same-day testing.
• Dengue fever: high fever, severe headache behind the eyes, muscle and joint pain and rash after travel to tropical regions.
• Typhoid, Zika, chikungunya and others depending on where you have been.
• Lyme disease and Rocky Mountain spotted fever: fever and headache after a tick bite, sometimes with a rash.

Non-infectious causes

• Giant cell arteritis: in people over 50, a new headache, scalp tenderness, jaw pain when chewing and low fever. It can cause sudden blindness, so it needs urgent assessment.
• Heat stroke: headache and high temperature after heat exposure, with confusion.
• Bleeding in the brain: a sudden, severe headache that may come with a low fever.

Viral illness vs meningitis

The glass test for rashes

Press the side of a clear drinking glass firmly against a rash. If the spots do not fade and remain visible through the glass, it may be meningococcal septicemia. Call 911 or your local emergency number. On darker skin, look at paler areas such as the palms, soles, inside the eyelids and the roof of the mouth.

How doctors find the cause

A doctor will ask when the fever and headache started, how severe the headache is, about travel, tick bites, contacts with illness, vaccinations and immune problems. They will check your temperature, neck stiffness, skin for rashes, ears, sinuses and throat, and do a neurological exam.

Depending on the findings, tests may include:

• swabs for flu, COVID-19 or strep
• blood tests: blood count, inflammation markers, blood cultures
• malaria blood films after travel
• a lumbar puncture (spinal tap) to test the fluid around the brain if meningitis or encephalitis is suspected
• a CT or MRI brain scan, especially with confusion, seizures or focal signs

Suspected bacterial meningitis is treated with antibiotics straight away, often before test results return.

Treating fever and headache at home

If the cause is a mild viral illness:

• Rest and stay home until you have been fever-free for 24 hours without medicine.
• Drink plenty of fluids: water, broths and oral rehydration solutions. Pale yellow urine is a good sign.
• Pain and fever relief: acetaminophen (paracetamol) or ibuprofen, following the label dose. Do not give aspirin to children or teenagers because of the risk of Reye syndrome. Avoid ibuprofen if you have kidney disease, stomach ulcers or are dehydrated.
• Dress lightly and keep the room comfortably cool.
• A cool cloth on the forehead may ease the headache.

Antiviral medicines for flu or COVID-19 work best when started within 2 days of symptoms in higher-risk people, so call your doctor early if you are over 65, pregnant or have a long-term condition.

Preventing infections that cause fever and headache

• Keep up to date with vaccines: meningococcal, pneumococcal, Hib, MMR, flu and COVID-19.
• Wash your hands regularly.
• Use insect repellent and malaria prevention when traveling to risk areas.
• Check for ticks after outdoor activities.

Frequently asked questions

What does a fever and headache together mean?

Most often it means a viral infection such as flu, COVID-19 or a cold, and it improves in a few days. Less commonly it points to sinusitis, strep throat, or a serious infection such as meningitis or encephalitis. Warning signs include a stiff neck, confusion, rash or seizure.

When is fever with headache an emergency?

Call 911 or your local emergency number for fever and headache with a stiff neck, a rash that does not fade under a glass, confusion, drowsiness, a seizure, sudden severe pain, or new weakness or speech problems. These can be signs of meningitis, encephalitis or bleeding in the brain.

How can I tell if my headache with fever is meningitis?

Meningitis typically causes a severe, worsening headache with a stiff neck, light sensitivity, vomiting and sometimes a non-fading rash or confusion. A viral illness headache is milder and eases with pain relievers. If you are unsure, seek urgent medical assessment, because early antibiotics save lives.

How long do fever and headache last with a virus?

With flu or a cold, fever usually lasts 2 to 4 days and the headache improves as the fever settles. Tiredness and a cough can last longer. Fever and headache lasting more than 3 days without improvement should be checked by a doctor.

What is the best medicine for fever and headache?

Acetaminophen (paracetamol) or ibuprofen both reduce fever and ease headache. Follow the label dose and do not exceed the daily limit. Do not give aspirin to children or teenagers. If pain relievers do not help, or warning signs appear, see a doctor.