What is a low-grade fever? How to know if you're sick and when to see a doctor

Ashley Laderer,Jason McKnightJan 30, 2021, 01:17 IST

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Your body develops a fever to make it harder for any disease cells to survive in your body.Boris Zhitkov/Getty Images

A low-grade fever happens when your body temperature is elevated, but still under 100.4°F.
Some causes of a low-grade fever include the common cold, the flu, a stomach virus, or a UTI.
But a low-grade fever in itself isn't necessarily a reason to worry, since a slightly elevated temperature won't hurt your body.

Many illnesses can cause a fever, which is when your body temperature rises over 100.4°F. In some cases, your body temperature may be elevated, but not quite as high as a fever. This is often referred to as a "low-grade fever" although it does not technically meet the definition of a fever.

Most of the time, low-grade fevers aren't a reason to worry. Many everyday ailments can cause a low-grade fever, including an ear infection or stomach bug. In rare cases, you can also have a low-grade fever with more serious infections.

Here's what you need to know about how to treat low-grade fevers and when you need to see a doctor.

What is a low-grade fever?

A low-grade fever is a body temperature that runs somewhere between your normal body temperature and 100.4°F, says Troy Madsen, MD, a professor of emergency medicine at the University of Utah.

However, there is some debate in the medical field about the exact body temperature that counts as a fever. "The definition may vary between 100.4 and 100.5 depending on the medical provider and the institution," Madsen says.

There is also some debate about the existence of a low-grade fever. While some providers accept the definition of a low-grade fever as anything between normal body temperature and 100.4°F, other providers believe that your temperature must be above 100.4°F to even count as a fever.

Your body temperature can shift based on factors like your age or the time of day, but for most people, a normal temperature falls anywhere between 97 and 99°F.

But when you get sick, your body heats up and develops a fever to make it harder for any disease cells to survive in your body. A low-grade fever can be a sign of an infection beginning in your body.

What causes a low-grade fever?

"The same infections which cause a typical fever may cause a low-grade fever, particularly if it's in the early stages of the infection," Madsen says.

Some infections that can cause a low-grade fever include:

If you have a severe infection like meningitis, your fever generally won't stay at the low-grade level for long. "In most cases, a serious infection will progress from a low-grade fever to a temperature of 100.5°F or greater within a day," Madsen says.

But infections aren't the only cause of low-grade fevers. There are several other reasons you may run a low-grade fever, such as:

You're exercising vigorously.
You're outside in hot weather or wearing heavy clothing.
You have an autoimmune disorder like rheumatoid arthritis.
You have recently had a flu vaccine.
You're feeling especially stressed.

In these situations, a rise in body temperature is a normal response and usually isn't a cause for concern, Madsen says. Along with a low-grade fever, you might sweat, have slight chills, develop a headache, or have a flushed face.

But if your low-grade fever comes with symptoms like extreme fatigue or confusion, this may be a cause for concern, Madsen says.

How to treat a low-grade fever

A low-grade fever in itself isn't necessarily a reason to worry, Madsen says, because a slightly higher temperature won't hurt your body.

But low-grade fevers can come with some uncomfortable symptoms that you may want to treat. "For example, you may have the early stages of a cold or the flu and have a low-grade fever with body aches and a sore throat," Madsen says.

Taking a dose of a non-steroidal anti-inflammatory drug like ibuprofen can help treat these symptoms and bring your temperature down as well. However, it's not necessary to take any medications unless your fever rises over 102°F.

If your low-grade fever is due to overheating, putting on loose-fitting clothing, resting in a cool space, or taking a cold shower may help bring your body down to a normal temperature.

No matter what is causing your fever, it's important to drink plenty of fluids. A low-grade fever generally won't cause severe dehydration, but you lose fluids more easily when your body temperature is higher. Drinking cold fluids can also help lower your body temperature.

It's also important to keep monitoring your temperature to see if it rises above 100.5 degrees and becomes an actual fever. You can take your temperature using a thermometer orally, rectally, or in your armpit.

When to see a doctor

"A low-grade fever in itself doesn't necessarily mean you need to see a doctor," Madsen says, "But if you're having other symptoms plus an elevated body temperature it may be a good time to call your doctor."

Be on the lookout for symptoms of an infection, as a bacterial infection may need to be treated with antibiotics. Madsen advises that some symptoms to look out for are:

Burning with urination
Difficulty breathing
Persistent cough
Congestion that doesn't improve after a week
Rash
Severe headache

For most adults and children, you should call your doctor if your temperature rises above 103°F. If you have an infant under 3 months old, you should call the doctor if their temperature rises above 100.4°F.

In very rare cases, people may run low-grade fevers for weeks or months, Madsen says. You shouldn't ignore this symptom, as it can be a sign of a cancer like lymphoma.

"If your body temperature just seems to be abnormally high over a longer period of time, it's a good idea to check in with your doctor, particularly if you're experiencing unexplained weight loss or extreme fatigue," Madsen says.

Insider's takeaway

A low-grade fever is a body temperature between 99 and 100.5°F. In most cases, a low-grade fever isn't anything to worry about and you can get relief from any symptoms by taking ibuprofen or drinking cold water.

However, if your fever keeps rising or you develop any unusual symptoms, reach out to your doctor to check that you don't have an infection or any other serious medical issue.

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