A fever starts at 100.4°F (38°C) and is your body’s natural way of fighting infection. Most fevers in adults and older children are harmless and resolve on their own within a few days. Your immediate priorities are staying hydrated, resting, and knowing which symptoms signal something more serious.
Why Your Body Runs a Fever
Fever isn’t the illness itself. It’s your immune system turning up the heat to fight off whatever is making you sick. Research from the National Institutes of Health shows that at fever temperatures (around 102°F), immune cells multiply faster and release more of the signaling molecules that coordinate your body’s defense. At the same time, the cells that normally dial down immune activity become less effective, letting your body mount a stronger response.
This is why mild fevers can actually be helpful. As immunologist Jeff Rathmell put it: “A little bit of fever is good, but a lot of fever is bad.” A sustained high fever increases DNA damage in cells, which is one reason chronic inflammation raises cancer risk over time. For a short-term illness, though, letting a low-grade fever do its work is a reasonable choice.
Getting an Accurate Temperature Reading
The thermometer you use and where you place it both affect your reading. Rectal thermometers are the most accurate but also the most invasive. Oral thermometers provide similar accuracy and are the practical choice for most adults and older children. Ear thermometers can be thrown off by earwax, ear infections, or an unusually shaped ear canal. Forehead thermometers are the least reliable: sweat, direct sunlight, cold air, and holding the device too far from the skin all introduce error.
Temperatures vary slightly depending on the measurement site, and there’s no reliable formula for converting between them. If you’re tracking a fever over time, use the same thermometer in the same spot each time so you can see a real trend.
Home Care That Actually Helps
The most important thing you can do during a fever is drink more fluids than usual. Your body loses extra water through sweat and faster breathing, roughly 10% more for every degree Celsius above 100.4°F. Water, broth, diluted juice, and electrolyte drinks all count. If your urine is dark yellow, you need more fluid.
Rest matters too. Your immune system works harder when you’re not diverting energy to other tasks. Stay home, sleep when you can, and wear lightweight clothing. Keep the room comfortable but not cold. A heavy blanket when you have chills will feel good in the moment but can trap heat and push your temperature higher.
You might be tempted to take a cool bath or sponge yourself down. Research comparing acetaminophen alone to acetaminophen plus a lukewarm sponge bath in children found that sponge-bathed kids cooled slightly faster in the first hour, but after two hours the temperatures were the same. The sponge bath group, however, was significantly more uncomfortable, with more crying, shivering, and goosebumps. Physical cooling methods are generally not recommended for fever. They’re reserved for hyperthermia, which is a different condition where the body overheats from external causes like heat stroke rather than infection.
When to Use Fever-Reducing Medication
You don’t need to treat every fever with medication. If you feel functional and your temperature is under 102°F, rest and fluids may be enough. Medication makes the most sense when your fever is making you miserable: you can’t sleep, you have a pounding headache, or your body aches are keeping you from resting.
The two standard options are acetaminophen (Tylenol) and ibuprofen (Advil, Motrin). For adults, follow the dosing on the package. Acetaminophen can be taken every 4 to 6 hours, with no more than 5 doses in 24 hours. Ibuprofen can be taken every 6 to 8 hours, with no more than 4 doses in 24 hours.
For children, always dose by weight rather than age. The packaging will have a weight-based chart. Don’t give acetaminophen to infants under 8 weeks old, and don’t give ibuprofen to infants under 6 months old unless directed by a pediatrician. Never give aspirin to children or teenagers, as it’s linked to a rare but serious condition called Reye’s syndrome.
Fevers in Babies and Young Children
The rules change significantly for infants. Any baby between 8 and 60 days old with a temperature of 100.4°F or higher needs medical evaluation, even if they look fine. The American Academy of Pediatrics has specific clinical guidelines for this age group because young infants can have serious bacterial infections without showing obvious symptoms. Don’t wait to see if the fever resolves on its own.
For older babies and toddlers, a fever alone isn’t necessarily alarming. Pay attention to how the child is acting. A toddler with a 101°F fever who is still playing and drinking fluids is less concerning than one with the same temperature who is limp, inconsolable, or refusing to drink. If your child has a febrile seizure (convulsions triggered by a rapid rise in temperature), seek immediate medical attention if it’s their first one. Call 911 if any seizure lasts more than five minutes or if your child doesn’t recover quickly afterward.
Warning Signs That Need Immediate Attention
Most fevers are part of a routine viral illness and pass within a few days. But certain symptoms alongside a fever point to conditions that need urgent care:
- Stiff neck with pain when bending your head forward, especially combined with a severe headache and sensitivity to bright light, which can indicate meningitis
- Mental confusion, altered speech, or strange behavior
- Difficulty breathing or chest pain
- Persistent vomiting that prevents you from keeping fluids down
- A new rash, particularly one that doesn’t fade when you press on it
- Pain when urinating, which may suggest a kidney infection
- Seizures or convulsions
- Abdominal pain
Adults with fevers of 103°F or higher will typically look and feel noticeably sick. At that level, medication to bring the temperature down is appropriate, and if the fever doesn’t respond or keeps climbing, seek medical care. A fever that persists beyond three days without improvement also warrants a call to your doctor, as does any fever that goes away and then returns after a day or two, since that pattern can signal a secondary infection.