Low temperature: definition, causes, treatment methods.


Most medical experts define subfebrile fever as a body temperature of 99 F to 100.3 F. Others use a less narrow definition, referring to subfebrile fever as a body temperature of 100 F to 102 F.

Typically, your body maintains a temperature around 98.6 F. Research shows that even in healthy people, normal body temperature can fluctuate up to 1.8 degrees F.

Normal body temperature can fluctuate depending on several factors. Some of these factors include how their temperature is measured (for example, orally or rectally), what time of day it is measured (their temperature is usually higher at night than in the morning), and where the person is menstruating. menstrual cycle .

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Other than fever, some people with a low fever will have no noticeable symptoms. Others may experience:

  • Headache
  • Fatigue
  • Muscle pain
  • Perspiration
  • Shaking chills
  • Loss of appetite
  • Decreased urine output


A high temperature, even a low temperature, is a sign that something is wrong with your body. Fever indicates that your immune system is strengthening its defenses against a foreign invader, be it a virus, bacteria, or other substance.

Experts are not entirely sure why the body reacts to infections and diseases with an increase in body temperature, but they believe that some disease-causing microbes are less likely to thrive at higher temperatures. They also suggest that an increase in body temperature can allow certain immune cells to seek out and destroy anything that attacks the body.

What are the common causes of low fever?


Both viral and bacterial infections can cause a mild fever. Some common culprits include:

  • Rhinovirus (also known as the common cold)
  • Flu
  • Viral gastroenteritis (also known as the stomach flu ). Examples of these include rotavirus , which is common in babies, and norovirus , which generally affects adults and is highly contagious.
  • Measles
  • Little pig
  • Chickenpox (varicella-zoster virus)
  • Rubella (also called German measles)
  • COVID-19
  • Urinary tract infections
  • Pneumonia
  • Ear infections
  • Strep throat
  • Cellulitis, an infection of the skin and surrounding tissues.
  • Escherichia coli (Escherichia coli) : While some strains of E. coli, the bacteria that live in your gut, are harmless, others can cause serious illness.
  • Sinus infections
  • Infectious mononucleosis (mononucleosis): This is a highly contagious disease that generally affects adolescents and young adults and is often caused by the Epstein-Barr virus.

Non-communicable diseases

Some autoimmune diseases, such as rheumatoid arthritis and lupus , can have a low-grade fever. In fact, up to 86% of people with lupus experience a fever, usually mild .

Some cancers (cancers) can cause cell changes in the body that lead to fever. Also, chemotherapy used to treat certain types of cancer can destroy disease-fighting white blood cells in your body, making you more susceptible to infections and the fevers that accompany them.

Other reasons

Other causes of low fever include:

  • Stress : Some people, especially young women, react to stress with an increase in body temperature. This is called a psychogenic fever.
  • Vaccines : Low fever is a common side effect of many vaccines , including flu shots and childhood vaccines. Fever is a sign that your body is developing immunity to disease. Fever can occur in 10% of children who receive routine childhood immunizations and in 70% of children who receive multiple vaccines .
  • Sensitivity to Certain Medications : Up to 7% of fever cases can be due to adverse reactions to certain medications, including antibiotics and medications used to treat seizures . This type of fever is called a drug fever.


You may blush and feel hot when you have a fever, but the only way to accurately determine your temperature is by measuring it with a thermometer.

Digital thermometers placed under the tongue or with a tip inserted into the anus (rectal temperature measurements are recommended for infants and very young children) provide the most reliable readings (change batteries periodically; spent batteries can lead to readings inaccurate) .

Thermometers placed under the armpit (called armpit thermometers) can give inaccurate readings. The same can be said for plastic strips, smartphone temperature apps, and fake thermometers .

Thermometers that scan the forehead or are placed inside the ear (called tympanic thermometers) can be used, but do not use a tympanic thermometer if you are measuring the temperature of an infant younger than 3 months or anyone with an ear infection.

One thing you shouldn't rely on when trying to find out if the temperature is there is touch. You can miss or underestimate a fever in up to 40% of people, even if the temperature reaches 102 F.

Watch out

A general rule of thumb is to treat a mild fever only if it makes you uncomfortable. And some experts say that won't happen until temperatures reach 102-103 F or higher.

There is also a fairly popular school of thought that by suppressing the fever, it also suppresses the immune system's production of white blood cells that destroy the disease, thus prolonging the disease.

If you want to treat a mild fever, acetaminophen (Tylenol) and ibuprofen (Advil) are good options (read package directions for correct dosage or consult your doctor).

Aspirin is another option, but never give aspirin to children or teens unless recommended by your healthcare provider. Aspirin use in this age group has been linked to a serious and life-threatening condition called Reye's syndrome .

Self-help measures include:

  • Water balance: A fever can cause your body to lose water (such as sweating or rapid breathing), increasing the chances of dehydration.
  • Resting
  • Wear light clothing
  • Eat light and easily digestible foods, such as broth soups.

When to call a practitioner

Most subfebrile temperatures go away within a few days and do not require medical attention. But be sure to call your doctor or go to the emergency room if any of the following conditions apply to you or someone you care for:

  • You have a child younger than 3 months with a fever (do not give antipyretic medications such as Children's Tylenol without consulting a doctor).
  • He has a fever and a stiff neck. It is a symptom of a life-threatening condition called meningitis that affects the brain and spinal cord.
  • You have a fever and a rash. These two combinations may indicate a serious illness, such as Toxic Shock Syndrome and Rocky Mountain Spotted Fever .
  • You feel dehydrated (signs include dry mouth, dry skin, sunken eyes, and dark urine).
  • Your child has a fever and seizures. Fever, especially when it rises rapidly, can sometimes cause so-called febrile seizures in young children.
  • You feel very bad.
  • You have a fever and severe pain or swelling anywhere in your body.
  • You experience painful urination or foul-smelling urine . This could be a sign of a urinary tract infection (UTI) that requires treatment with antibiotics.
  • You are disoriented.
  • Your temperature lasts more than two days.


The best way to prevent fever is to prevent the infections that cause it:

  • Wash your hands regularly with soap and water for 20 seconds, especially after using the bathroom and changing diapers and before preparing or eating.
  • To prevent urinary tract infections, urinate before and after having sex, drink plenty of fluids, and wipe from front to back after having a bowel movement.
  • Be on the lookout for vaccinations. Yes, some vaccines can cause a mild fever in some people. But that may be a small price to pay for the protection they offer against serious or life-threatening illnesses.
  • Avoid touching your eyes, mouth, and nose, which are the main entry points for germs.

Get the word of drug information

Any fever can be stressful. But it is important to remember that most mild forms of fever are harmless and go away after a few days or even sooner. If your symptoms bother you, you can try over-the-counter fever medications. However, don't hesitate to call your doctor if you are concerned about any of your symptoms or just want to ask for advice and encouragement.

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