A fever has always been somewhat of a "red flag" symptom when it comes to illness — and concern over fever has increased over the last few years with the COVID-19 pandemic, given that it's one of the telltale symptoms [1]. But having a fever above normal adult temperature is not always a sign to panic.

According to the Centres for Disease Control and Prevention (CDC) [2], the presence of a fever typically indicates an infectious disease, and if your body is fighting off a viral or bacterial infection, a fever can be one of the first signs, says Soma Mandal, MD [3], a board-certified internist at Summit Health in New Jersey. Fortunately, most fevers can be self-managed with over-the-counter medications, rest, and fluids. But other fevers can be stubborn and are more cause for concern.

Ahead, get a comprehensive breakdown on adult fevers, normal adult temperature, fever symptoms in adults, how to reduce fever in adults, and when to worry about adult fevers.

What's a Normal Adult Temperature?

According to Dr. Mandal, a normal body temperature is typically around 98.6 degrees Fahrenheit, but this can vary from person to person. "Typically, a low-grade fever is 99 degrees Fahrenheit, and anything that is 100.4 F or above is typically considered to be a fever," she explains.

What Causes Fever in Adults?

As mentioned earlier, a fever often indicates the presence of a viral or bacterial infection that your body is working to fight.

But extreme heat can raise body temperature and manifest as fever, too, Dr. Mandal says. Sweating and dilating blood vessels are some of the body's natural cooling mechanisms, but if these mechanisms are not enough, a fever might crop up.

Additionally, certain medications such as antibiotics, antimalarial medications, and anesthesia can also cause fever, Dr. Mandal adds. "With drug-induced fevers, the fever usually goes away a few days after stopping the medication," she says.

Surgery can also trigger inflammatory proteins and cause postoperative fever, and hormonal conditions like a hyperactive thyroid can cause fever, fast heart rate, and fluctuating blood pressure, Dr. Mandal adds. Other conditions that cause inflammation, like rheumatoid arthritis and lupus, can trigger a fever response as well.

Fever Symptoms in Adults

Feeling warm and having a thermometer show a body temperature that's above normal or average aren't the only signs of a fever. According to Cleveland Clinic, other fever symptoms [4] include:

• Chills, shivering, or shaking
• Body aches or headaches
• Fatigue or tiredness
• Sporadic or constant sweating
• A flushed face or hot skin

Recurrent Fever in Adults

"A recurring fever is a fever that happens multiple times over a period of time," per Cleveland Clinic [5]. These fevers are also usually episodic, meaning they come and go. They are most common in children. But in adults, recurrent fevers can be caused by an untreated infection, periodic fever syndromes [6] (a group of disorders that can trigger recurrent fevers), chronic illnesses like lupus and arthritis, stress, changes in sleep, and certain medications, according to DM Clinical Research [7].

How to Reduce Fever in Adults

Of course, fever-reducing medications [8] like acetaminophen (aka Tylenol) are often considered a go-to form of treatment. But not all fevers need medical treatment, Dr. Mandal says. Sometimes, resting and drinking plenty of fluids [9] can do the trick if the fever is below 102 degrees, according to Mayo Clinic.

When to Worry About Fever in Adults

If you're just a couple of decimal points higher than the standard 98.6, you typically don't need to worry. But if your fever starts creeping up into the 100s, here's what you need to know:

• Less than 101 fever in adults: No medical treatment is required, per Cleveland Clinic [10].
• 101 fever in adults: This is considered a moderate-grade fever and can usually be treated at home, per Tylenol [11].
• 102 fever in adults: Try home treatments first, and contact your healthcare provider if the fever does not go away within a few days, according to Cleveland Clinic.
• 103 fever in adults: Contact your healthcare provider, particularly if the fever has lasted two hours after home treatment, Cleveland Clinic states.
• 104 fever in adults: A temperature at or above 104 is called hyperpyrexia and is considered a medical emergency, per Tylenol [12].
• 105 fever in adults: Contact your provider right away if your fever reaches 105, per Penn Medicine [13].
• 106 fever in adults: Any fever above 105 that has not come down with treatment is considered "a life-threatening medical emergency and you should call 911," Cleveland Clinic states.

You should also seek medical attention if your fever is accompanied by any of the following symptoms, as it can be a sign of something more serious, per Mayo Clinic [14]:

• Severe headache
• Rash
• Unusual sensitivity to bright light
• Stiff neck and pain when you bend your head forward
• Mental confusion, strange behaviour, or altered speech
• Persistent vomiting
• Difficulty breathing or chest pain
• Abdominal pain
• Pain when urinating
• Convulsions or seizures