The 99.8 Fever – What You Need to Know About Low Grade Fevers

What is a Fever?

Generally speaking, a normal oral temperature for a resting, healthy adult is about 98.6°F (37°C). However, “normal” can vary based on age, race, and other factors. For instance, in an individual > 70 years old, a normal temp could be lower at 96.8°F (36°C). Furthermore, a person’s temperature is actually lowest in the morning and highest in the afternoon. It can also fluctuate based on one’s activity level (e.g. if one is exercising), one’s environment (hot, cold, etc.), hydration status, or even medications that he/she may be taking.

Fever is a sign of inflammation, meaning that it most commonly indicates that there is an underlying illness or even a bodily injury. As a result of this, we most often associate fevers with the flu or the cold. However, fevers may be seen with any type of infection (skin infection, pneumonia, etc.) and may also be associated with certain autoimmune diseases. Less commonly, it may be caused by certain medications that one is taking.

It is important to keep in mind, however, that a fever, in and of itself, is not a disease.

A fever appears to be one way your body fights an underlying illness i.e. your body raises its temperature via its internal thermostat (located within a portion of the brain called the hypothalamus) to help your immune system to defeat an infection.

The CDC defines a fever as a temperature over 100.4 (38). Please refer to this article for further information regarding fevers.

What is a Low-grade Fever? 

However, what if your temperature is only mildly elevated?

For instance, a temperature of 99.8, is oftentimes referred to as a low-grade fever (this range is typically 99 – 100.4).  

There really is no consensus agreement on how to manage a low-grade fever. In other words, we don’t have clear cut answers on how to manage or treat a low-grade fever. This is mainly because low-grade fevers usually are not a cause for alarm and most often are not associated with any serious conditions.

That being said, it is still important to understand low-grade fevers, what they mean, and what you can do about them.

What are the different “types” of Fevers? 

There’s a bit of a gray area when it comes to assessing fevers, particularly, low-grade ones. As was discussed prior, “normal” temperatures can vary based on age, race, and other factors. Furthermore, a person’s temperature can differ based on the time of day. For instance, temperatures are actually lowest in the morning and highest in the afternoon. Temperature can also fluctuate based on one’s activity level (e.g. if one is exercising), one’s environment (hot, cold, etc.), hydration status, or even medications that he/she may be taking. Finally, temperatures can vary depending on where the temperature is being taken. Take a look at this table below:

SiteLow Grade FeverModerate FeverHigh Fever
AdultChildAdultChildAdultChild
Axillary98.6-99.899.5-100.4100.5-101.3100.5-103.5≥101.2≥103.5
Temporal99-100.499-100.4100.4-101.3100.5-103≥101.2≥103
Rectal99-100.4100-100.4101.5-102.2100.5-103≥102.2≥103
Oral98.6-100.499.5-100.4100.5-101.3100.5-103.5≥101.2≥103.5
Ear99-100.4100-100.4100.4-101.3100.5-103≥101.2≥103.5

Keep in mind that when a child reaches the age of 36 months or three years, you should start using the adult fever readings to determine the presence of a fever.

Based on the chart above, a low-grade fever can be defined as a temperature that’s between normal body temperature and a fever.

Clear as mud, right?

In general, rectal temperatures are the most accurate and should be used to measure temperatures in infants. Otherwise, an oral temperature is usually the most accurate.

Most importantly, if you have any concern that you or your loved one has a low-grade fever, particularly if it is prolonged or associated with any concerning symptoms, you should call your health care professional to discuss the appropriate next steps.

What Typically Causes a Low Grade Fever?

Remember that a fever is a sign of inflammation, meaning that it most commonly indicates that there is an underlying illness or even a bodily injury. As a result of this, we most often associate fevers with the flu or the cold. However, fevers may be seen with any type of infection (skin infection, pneumonia, etc.) and may also be associated with certain autoimmune diseases. Less commonly, it may be caused by certain medications that one is taking.

It is important to understand that a fever differs from hyperthermia. A fever appears to be one way your body fights an underlying illness i.e. your body raises its temperature via its internal thermostat (located within a portion of the brain called the hypothalamus) to help your immune system to defeat an infection. On the other hand, hyperthermia happens because your body is overheating. This most commonly happens when you are exercising on a really hot day.

In this context, while a low-grade fever may indicate the beginning of our system’s defense against potential threats current research, while limited, suggests that in most cases, low-grade fevers are safe and do not indicate any significant underlying infection or injury.

That being said, if you have any concern that you or your loved one has a low-grade fever, particularly if it is prolonged or associated with any concerning symptoms, you should call your health care professional to discuss the appropriate next steps.

Other Possible Causes of a Low Grade Fever

Again, as mentioned above, in most cases, a low-grade fever is not concerning.

However, although uncommon, besides an infection there are a number of other causes for a prolonged low-grade fever. These include, but are not limited to:

  • Arthritis
  • Vasculitis
  • Cancer
  • Heat stroke
  • Immunization rejection
  • Stroke
  • Pulmonary embolism
  • Myocardial infarction (heart attack)
  • Drug reaction
  • Autoimmune disease

Again, if you have any concern that you or your loved one has a low-grade fever, particularly if it is prolonged or associated with any concerning symptoms, you should call your health care professional to discuss the appropriate next steps.

When Should You Worry About a Low Grade Fever?

Again, as mentioned above, in most cases, a low-grade fever is not concerning, particularly in the absence of any associated symptoms.

Even if accompanied by mild symptoms (cough, body aches, runny nose, etc.), as a general rule of thumb, simple steps like getting more rest, staying hydrated, and taking over-the-counter fever reducers (if you feel uncomfortable) is all that is needed until the fever resolves.

However, if you’ve been experiencing a low-grade fever for several days or have any of the following symptoms, you should call your health care professional or 911 to discuss the appropriate next steps:

  • Chills
  • Generalized weakness
  • Vomiting
  • Bloody stool
  • Altered consciousness
  • Sore throat
  • Shortness of breath
  • Body pain
  • Diarrhea or constipation
  • Loss of appetite
  • Skin color changes
  • Rashes
  • Seizures

Treating a Low Grade Fever

In most cases, a low-grade fever will not need treatment. Again, most often it is more the result of changes in your internal temperature versus the activation of your body’s defense mechanisms. However, as mentioned above, if it is accompanied by mild symptoms (cough, body aches, runny nose, etc.), as a general rule of thumb, simple steps like getting more rest, staying hydrated, and taking over-the-counter fever reducers (if you feel uncomfortable) is all that is needed until the fever resolves. Furthermore, there are a lot of over the counter home remedies which may offer some relief.

Here are a few simple treatment methods you can use to address a low fever in the presence of associated symptoms:

  • Stay hydrated.
  • If accompanied by headaches, muscle aches, an over the counter anti-inflammatory like acetaminophen (Tylenol) or ibuprofen (Advil) can be helpful.
  • Eat healthy
  • Stay warm
  • Humidifiers can help with symptoms of congestion (e.g. stuffy nose)

In Closing

In most cases, a low-grade fever is not concerning, particularly in the absence of any associated symptoms.

Even if accompanied by mild symptoms (cough, body aches, runny nose, etc.), as a general rule of thumb, simple steps like getting more rest, staying hydrated, and taking over-the-counter fever reducers (if you feel uncomfortable) is all that is needed until the fever resolves.

However, if you’ve been experiencing a low-grade fever for several days or have any concerning symptoms as mentioned above, you should call your health care professional or 911 to discuss the appropriate next steps.


Dr. Andrew Chung

Dr. Andrew Chung is a Spine Surgeon at Sonoran Spine in Tempe, Arizona. He is a graduate of the Philadelphia College of Osteopathic Medicine and was formerly Spine Surgeon Clinical Fellow at Cedars-Sinai, Spine Surgery Fellow at Keck Hospital, University of Southern California and Chief Resident and an Instructor of Orthopedic Surgery in the Department of Orthopedic Surgery at the Mayo Clinic in Arizona. Dr. Chung's research.