A fever is when your body temperature rises above its normal range. Most people have a normal body temperature around 98.6°F (37°C), but this can vary slightly from person to person. A fever is typically defined as a temperature of 100.4°F (38°C) or higher when measured orally (in the mouth). Some medical sources consider temperatures between 99.5°F and 100.3°F a low-grade fever.
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Your body's temperature is controlled by a part of the brain called the hypothalamus, which acts like a thermostat. When you have an infection or illness, your immune system releases chemicals called pyrogens that signal the hypothalamus to raise your body's temperature set point. This is actually your body's natural defense mechanism—fevers help fight infections by making your body a less comfortable environment for bacteria and viruses to survive.
Fevers are not a disease themselves but a symptom of an underlying condition. Common causes include the common cold, influenza (flu), ear infections, urinary tract infections, strep throat, and other bacterial or viral infections. Non-infectious causes can also trigger fevers, such as certain medications, autoimmune diseases, heat exhaustion, or reactions to vaccinations.
It is important to recognize that a fever can actually be beneficial in fighting infection. Research shows that moderate fevers may help your immune system work more effectively. However, very high fevers (above 103°F or 39.4°C) can be dangerous and may cause complications, particularly in young children and older adults. Understanding what a fever is helps you recognize when one may require medical attention and when home care may be appropriate.
Practical Takeaway: Track your temperature with a reliable thermometer and note when you took the reading and how you measured it (oral, under the arm, etc.). This information is valuable if you need to contact a healthcare provider.
Accurate temperature measurement is essential for knowing whether someone actually has a fever and how high it is. There are several types of thermometers available, each with different levels of accuracy. Digital thermometers are the most commonly recommended and widely available. They work by using a heat sensor to detect temperature and display it on a digital screen. Digital thermometers can be used orally (under the tongue), rectally (in the rectum), or axillary (under the arm).
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Oral measurement is the most common method for adults and older children. To measure temperature orally, place the thermometer tip under the tongue, close your mouth, and keep it there for the time recommended by the thermometer manufacturer—usually 30 to 60 seconds. Wait at least 15 minutes after eating, drinking, or smoking before taking an oral temperature, as these activities can affect the reading. Rectal temperature measurement is considered the most accurate method, especially for infants and young children under three years old. This requires inserting the thermometer into the rectum about a half-inch to one inch, depending on the child's age. Axillary (under-arm) measurement is less accurate but is a non-invasive option. Hold the thermometer under the arm for about three to four minutes to get a reliable reading.
Infrared thermometers, which measure heat from the eardrum or forehead, are quick and convenient but can be less accurate if not used correctly. Temporal artery thermometers (forehead thermometers) are increasingly popular but require you to follow the specific instructions for your device. Avoid glass mercury thermometers, which are accurate but can break and release toxic mercury.
When measuring temperature, record the time and method used. If someone has a fever, take their temperature again after an hour or two to see if it is increasing, decreasing, or staying stable. For infants under three months old, any temperature of 100.4°F (38°C) or higher requires medical attention regardless of other symptoms, so contact a healthcare provider immediately.
Practical Takeaway: Keep a reliable digital thermometer accessible at home, know how to use it correctly, and write down temperature readings with the date and time to track patterns over hours or days.
Not all fevers require a visit to a doctor or emergency room, but certain situations do call for medical attention. For infants under three months old, any fever of 100.4°F (38°C) or higher is considered a medical concern and should be reported to a pediatrician or evaluated at an emergency facility. The immune systems of very young infants are still developing, and they cannot show early signs of serious illness as clearly as older children or adults.
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For children between three months and three years old, a fever of 102.2°F (39°C) or higher lasting more than one day, or any fever lasting longer than five days regardless of temperature, warrants a call to your child's pediatrician. Similarly, if a child has a fever along with other concerning symptoms—such as difficulty breathing, unusual sleepiness, stiff neck, severe abdominal pain, unexplained rash, or signs of dehydration—seek medical care promptly.
For adults, most fevers resolve without treatment and do not indicate a serious problem. However, contact a healthcare provider if you have a fever of 103°F (39.4°C) or higher, a fever that lasts longer than three days, a fever accompanied by severe symptoms such as difficulty breathing, chest pain, severe headache, confusion, or stiff neck. You should also seek care if you have a weakened immune system (from conditions like HIV, cancer treatment, or certain medications), are pregnant, or are an older adult with underlying health conditions.
Additionally, contact a healthcare provider if the fever is accompanied by a rash that does not blanch (turn white) when you press on it, if there are signs of meningitis or other serious conditions, or if you are concerned about the severity of symptoms. Trust your instincts—if something feels seriously wrong, it is better to contact a medical professional than to wait. Many healthcare providers offer phone or telehealth consultations, which can be a good option for getting medical input without leaving home.
Practical Takeaway: Know your local healthcare provider's phone number and after-hours contact information. Save it in your phone or keep it posted at home so you can reach someone quickly if you have questions about whether medical care is needed.
When someone has a mild to moderate fever without other serious symptoms, home care can help manage discomfort while the body fights infection. The primary goal of home care is to make the person feel more comfortable, not necessarily to bring the temperature down quickly. In fact, trying to suppress all fever may actually interfere with the body's natural defense mechanism.
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Rest is one of the most important elements of fever care. Your body uses significant energy to mount an immune response, so adequate rest helps your body direct resources toward fighting the infection. Encourage the person with a fever to rest in a cool, comfortable room. Keep the environment at a comfortable temperature—not too hot or cold. Some people with a fever feel cold and want to bundle up in blankets, while others feel hot and want to cool down. Follow the person's comfort level, but avoid overheating, which can make the fever go higher.
Staying hydrated is crucial when you have a fever. Fever increases fluid loss through perspiration and breathing, which can lead to dehydration. Encourage drinking water, clear broths, herbal tea, or electrolyte beverages. For children, oral rehydration solutions specifically formulated with the right balance of electrolytes and fluids are often helpful. Avoid alcohol and caffeinated beverages, as these can increase fluid loss. Offer small amounts of liquid frequently rather than large amounts at once, which may be easier to tolerate.
Light, nutritious food can support recovery, but do not force eating if the person is not hungry. Offer foods that are easy to digest and appealing, such as soup, crackers, yogurt, fruit, or toast. Maintain good hygiene by washing hands frequently to prevent spreading illness to others. If you are caring for someone with a fever, wash your hands after contact and maintain distance to reduce transmission risk.
Practical Takeaway: Create a comfortable "recovery space" with access to water, tissues, a thermometer, and entertainment. Keep a list of fever-friendly foods and beverages on hand so you can provide options without having
This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.