Most fevers run their course in one to three days and don’t need anything beyond rest, fluids, and basic comfort measures. A fever starts at 100.4°F (38°C) when measured rectally or with an ear thermometer, or 100°F (37.8°C) orally. Your body raises its temperature on purpose to fight infection, so the goal isn’t always to eliminate the fever. It’s to stay comfortable and watch for signs that something more serious is going on.
Why Your Body Runs a Fever
When your immune system detects an infection, it releases signaling molecules that reach a temperature-control center deep in your brain. This region acts like a thermostat. Normally it keeps your body close to 98.6°F, but during an infection it essentially raises the set point. Your brain then triggers responses to generate heat: shivering, narrowing of blood vessels near the skin, and an increased heart rate. That’s why you can feel freezing cold even though a thermometer says you’re running hot. Your body is actively trying to reach that new, higher target temperature.
This elevated temperature makes it harder for many bacteria and viruses to reproduce, and it speeds up some immune responses. In most cases, the fever itself isn’t dangerous. It’s a symptom, not a disease.
Staying Hydrated
Fever increases fluid loss through sweating and faster breathing, so dehydration is one of the most common complications. Drink water, diluted juice, or broth throughout the day. You don’t need to force large amounts at once. Small, frequent sips work well, especially if nausea is an issue.
For infants under one year, an oral rehydration solution like Pedialyte is a better choice than plain water because it contains the right balance of salts and sugars to replace what’s being lost. Older children and adults generally do fine with water and light snacks, though electrolyte drinks can help if appetite is low and fluids are all that’s going in.
Over-the-Counter Fever Reducers
Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) are the two main options. You don’t have to take either one if your fever is mild and you feel okay. Their purpose is comfort, not cure. If body aches, chills, or a headache are making you miserable, they can bring your temperature down and help you rest.
For adults, acetaminophen can be taken every four to six hours. The critical safety limit is 4,000 milligrams in 24 hours, which is easier to exceed than most people realize since acetaminophen is an ingredient in many cold and flu products. Ibuprofen is typically taken every six to eight hours and should be taken with food or milk to prevent stomach irritation.
Fever Reducers for Children
Children’s doses are based on weight, not age. Always use the dosing chart on the packaging or one provided by your pediatrician. A few important restrictions to keep in mind:
- Acetaminophen should not be given to infants under 8 weeks old. It can be repeated every 4 to 6 hours, up to 5 times in 24 hours.
- Ibuprofen should not be given to infants under 6 months old. It can be repeated every 6 to 8 hours, up to 4 times in 24 hours. Avoid it if the child is vomiting, dehydrated, has stomach pain, or has been exposed to chickenpox in the past 21 days.
Use a measuring syringe rather than a kitchen spoon. A half teaspoon is 2.5 ml, and the difference between that and a full teaspoon (5 ml) matters at pediatric doses. Never give aspirin to children or teenagers, as it carries a risk of a rare but serious condition called Reye’s syndrome.
Comfort Measures That Help
Dress in light, breathable layers. If you’re shivering and cold, it’s fine to use a blanket, but don’t pile on heavy quilts. Overheating yourself to the point of heavy sweating can worsen dehydration without actually helping the fever resolve faster.
A room-temperature bath or shower that feels slightly cool to the touch can offer some relief. Skip ice baths, cold packs, and alcohol rubs. Research on tepid sponge baths in children found they caused significantly more discomfort without producing a meaningful temperature reduction over a two-hour period compared to medication alone. Physical cooling methods aren’t generally recommended for fever. They can trigger more shivering, which actually generates heat.
Rest matters more than anything else. Your immune system works best when you’re not pushing through a workout or a full day at the office. Sleep as much as your body wants to.
Fever in Babies and Young Children
The rules are stricter for infants. Any baby under 8 weeks old with a rectal temperature of 100.4°F or higher needs to be seen by a doctor right away, even if the baby seems fine otherwise. The American Academy of Pediatrics has specific evaluation guidelines for infants 8 to 60 days old with fever, which may include blood work and urine tests to rule out bacterial infections. For very young babies, fever is treated as a serious finding until proven otherwise.
For older babies and toddlers, a rectal thermometer gives the most accurate reading. Ear and forehead (temporal artery) thermometers are convenient but can be less reliable in small children. Armpit readings tend to run lower: a reading of 99°F or higher under the arm is considered a fever.
Febrile Seizures
Some children between six months and five years old experience seizures triggered by fever. These are called febrile seizures, and while they look frightening, they’re usually harmless. Symptoms include uncontrollable shaking, eyes rolling back, loss of consciousness, and sometimes drooling or vomiting. A simple febrile seizure typically lasts a few seconds to a couple of minutes.
If your child has a seizure, lay them on their side on a flat surface, don’t put anything in their mouth, and time the episode. Any first-time seizure needs medical evaluation. Get emergency care if a seizure lasts longer than 15 minutes, happens more than once in a day, or only affects one side of the body.
Warning Signs That Need Medical Attention
Most fevers in otherwise healthy people aren’t emergencies. But certain symptoms alongside a fever point to something that requires prompt care. The American College of Emergency Physicians identifies these red flags:
- Stiff neck that resists movement, especially with sensitivity to light
- Severe headache that doesn’t respond to over-the-counter medication
- Confusion, altered speech, or difficulty waking up
- Seizures or convulsions
- Difficulty breathing
- Rash that looks like small bleeding spots under the skin
- Persistent vomiting or abdominal pain
For adults, a fever above 103°F that doesn’t come down with medication, or any fever lasting more than three days, warrants a call to your doctor. For children, a temperature at or above 100.4°F in an infant under three months is always an immediate concern, regardless of other symptoms. In older children, persistent high fever, lethargy, or refusal to drink fluids are reasons to seek care sooner rather than later.