The normal human body temperature is about 98.6℉ (37℃), but that can fluctuate up or down. When that happens, your body uses thermoregulation to bring your temperature back to normal.

How does thermoregulation work?

Thermoregulation is controlled by the hypothalamus, which is a small structure in your brain. If the hypothalamus senses your body’s temperature is too high or low, it sends signals to your nervous system, muscles, organs, and glands. These signals help cool you down or warm you up. 

If your internal temperature is too high, your body may cool you down through:

  • Sweating. Your body’s sweat glands release sweat onto your skin.
  • Vasodilation. Your body’s blood vessels get wider to increase blood flow to your skin. 

If your internal temperature is too low, your body may warm you up through:

  • Vasoconstriction. Your body’s blood vessels narrow to decrease blood flow to your skin.
  • Thermogenesis. Your body’s organs produce heat in order to keep you warm.
  • Hormonal thermogenesis. Thyroid glands in your body release hormones to increase your metabolism.

Younger children may have a harder time regulating their temperature than adults do. Additionally, research shows that older adults may have a harder time regulating than younger adults. That’s because they sweat less and it takes them longer to start sweating compared to younger adults. 

Fevers

A fever happens when your temperature is higher than normal. In adults, a fever is considered to be anything above 100.4℉ (38℃).

Causes

Fevers are mostly caused by infections that your body is trying to fight off. You may also develop a fever from:

  • Medications including some antibiotics, blood pressure medicines, and anti-seizure medicines
  • Heat illness
  • Some cancers
  • Autoimmune diseases
  • Some childhood immunizations such as diphtheria or tetanus
  • Blood clots
  • Food poisoning

Symptoms

Fever symptoms may be different depending on the cause of the fever. You may notice unusual hot and cold shifts in your body temperature. You may also notice:

  • Sweating
  • Shivering
  • Muscle weakness
  • Dehydration
  • Headache
  • Appetite loss 

Treatment

For the most part, fevers can be treated at home. The amount of care and treatment you’ll need depends on the severity of the fever.

Drinking a lot of water and getting enough rest is sometimes all it takes to feel better. You can help regulate your body temperature during a fever by:

  • Resting inside where the temperature is comfortable
  • Taking a bath with lukewarm water
  • Drinking a lot of water and other fluids
  • Taking ibuprofen (Advil) or acetaminophen (Tylenol) 

See a doctor

A fever can sometimes be a symptom of a more serious health condition. If your fever is over 103 (39.4) or lasts for more than 3 days, see a doctor.

Heat intolerance

Heat intolerance is a hypersensitivity to heat and an inability to regulate your temperature when you’re hot. You may have heat intolerance if you find yourself constantly uncomfortable in the heat.

Medications are one of the most common causes of heat intolerance. Allergy, blood pressure, and decongestant medications may disrupt the blood flow to your skin and prevent sweating that would normally cool you down.

Other causes of heat intolerance include:

  • Caffeine
  • Hyperthyroidism
  • Multiple sclerosis (MS) 

Symptoms of heat intolerance include:

  • Nausea
  • Dizziness
  • Headache
  • Muscle weakness
  • Muscle cramps
  • Fast heartbeat

In less common cases, symptoms of heat intolerance may lead to heat exhaustion, which can lead to heat stroke if not properly treated. Symptoms of heat exhaustion include:

  • Fast breathing and heart rate
  • Muscle cramps
  • Nausea and vomiting
  • Confusion
  • Loss of consciousness
  • Body temperature above 104℉ (40℃)

You can help treat and prevent heat intolerance by keeping yourself hydrated, wearing lightweight clothes, and staying in a cool environment. 

If you have symptoms of heat exhaustion, it’s important to get evaluated by a medical professional as soon as possible to prevent heat stroke. Heat stroke is a medical emergency.

The takeaway 

It’s very easy for your body temperature to shift. Something as simple as stepping outside in the cold may cause your temperature to drop. Your body then uses thermoregulation to bring your temperature back to normal.