Updated July 2021
A fever isn’t always a problem. Defined as a temporary increase in body temperature, a fever is just a symptom, not an illness.
In fact, sometimes a fever can be a good thing: It’s often a sign that your body is fighting an infection or illness. But how do you know when a fever is dangerous? When is it time to see a doctor for a high temperature?
What Is a Fever?
A fever is a higher-than-normal body temperature.
Normal body temperature is 98.6 degrees Fahrenheit, and anything above 99.5 F (when measured orally with a thermometer) is considered a fever in both children and adults.
Your body temperature can rise naturally throughout the day and is usually higher in the evening. A number of other factors can increase body temperature, but these factors are not considered fever-inducing. Things like physical exertion, heavy clothing, high humidity and heat, strong emotions, and certain medications can trigger your body temperature to rise. If you’re a woman on your menstrual cycle you may also experience a higher body temperature.
Why You Have a Fever
A fever typically occurs in response to infection, when your body’s immune system is fighting off bacteria or a virus. The increased body heat makes it more difficult for bacteria and viruses to survive. Fevers also activate your immune system, which fights off diseases.
Common causes of fever include:
- Colds and flu
- Ear infections
- Sinus infections
- Skin infections
- Bladder and urinary-tract infections
- Blood clots
- Rheumatoid arthritis
- Inflammatory bowel disease
- Cancer, especially lymphoma and leukemia
- Teething (in children)
- Immunizations (in children)
When to Seek Help: How to Know When a Fever Is Dangerous
You should seek medical attention for yourself or a child under the following fever scenarios:
- If your child is 3 months old or younger and has a rectal temperature of 100.4 degrees F or higher
- If your child is 3 to 12 months old and has an oral temperature of 102.2 degrees F
- If your child is 2 years old or younger and has a fever that lasts longer than 24 to 48 hours
- Adults with a fever higher than 105 degrees F or a fever over 103 degrees F that rises or lasts longer than 48 hours
In addition, you should seek medical care if you have a fever accompanied by rash and bruising, difficulty breathing, and/or pain while urinating. Also consult a doctor if you have recently been vaccinated, visited another country, or have a serious pre-existing illness. Seek out a pediatrician if your child seems confused, has a stiff neck, and/or won’t stop crying.
High Fever Risks
In most cases, fevers can break on their own or with home remedies. However, high fevers that linger or worsen can cause significant health complications if left untreated, including febrile seizures, brain damage, and even death.
If an illness is causing your fever, that illness may come with side effects and complications of its own.
High Fever Symptoms
If you have a fever, you may experience related symptoms that include:
- Headache/body aches
- Lack of appetite
High fevers can come with serious symptoms. You should contact your doctor if you experience them:
- Breathing problems
- Cognitive issues or confusion
- Loss of consciousness
- Severe pain, especially in the head, chest, or stomach
- Pain while urinating
- Rash or bruises
- Stiff neck
- Urinary discharge
How to Lower a Fever
For most adults and kids with a mild fever under 102 degrees F, rest is the best solution. You can try to lower the fever yourself with some simple steps that work for both children and grownups:
- Remove heavy clothing and blankets and keep surroundings cool but not cold
- Take a lukewarm bath
- Take acetaminophen as directed, but do not give young children aspirin
- Drink plenty of fluids
- Avoid ice baths and alcohol rubs, which can cause shivering and in turn raise body temperature further