You feel cold with a fever because your brain raises your body’s temperature set point, so your normal temperature feels cold.
Why
Pyrogens from infection raise the hypothalamus’s temperature set point. Your body then feels cold until it reaches the new level. It triggers shivering and constricted blood vessels to create heat.
Fever
Defined as 100.4°F (38°C) or higher.
What to do
- Rest and drink fluids.
- Use a light blanket.
- Take acetaminophen or ibuprofen.
See a doctor
For fever over 103°F, lasting more than 3 days, or fever in a baby under 3 months.
The thermostat shift
Fever occurs when the hypothalamus resets the body’s “thermostat” to a higher temperature in response to infection, driven by chemicals called pyrogens (such as interleukin-1). Your actual body temperature is lower than the new set point, so you feel cold and shiver to produce heat.
Chills and shivering
Muscles contract rapidly to create heat, and blood vessels in the skin constrict to preserve heat. This is why skin feels cold and goose bumps appear. Chills often come before the temperature peaks.
Phase of fever
When the fever breaks, the set point returns to normal, and you feel hot, flush and sweat as the body cools.
Definition
Fever in adults is generally a temperature of 100.4 degrees F (38 degrees C) or higher.
What to do
- Rest and drink fluids.
- Use light blankets, not heavy ones, once chills pass.
- Take acetaminophen or ibuprofen to ease discomfort, per label directions.
- Do not give aspirin to children or teenagers due to the risk of Reye syndrome.
- Avoid cold baths or alcohol rubs.
- Dress in light layers.
Fever is a defense
Moderate fever can help the immune system fight infections. Treating fever is mainly for comfort.
See a doctor if
- Adult temperature above 103 degrees F (39.4 degrees C), or fever lasting more than 3 days.
- Fever with stiff neck, severe headache, rash, confusion, trouble breathing, chest pain, persistent vomiting or severe abdominal pain.
- Infants under 3 months with a temperature of 100.4 degrees F or higher need immediate evaluation.
- Fever in people with weakened immune systems or recent travel.
Febrile seizures
They affect 2% to 5% of young children and are usually harmless, but call a doctor.
Why chills come with fever
A fever starts when pyrogens, substances released by infection or inflammation, such as interleukin-1, interleukin-6 and prostaglandin E2, reset the hypothalamus thermostat to a higher temperature. The body then feels cold because its temperature is below the new set point, and it shivers, narrows blood vessels in the skin and seeks warmth to raise temperature. When the fever breaks, the set point returns to normal, and you feel hot and sweat. A fever is generally a temperature of 100.4 F (38 C) or higher.
What to do and warning signs
Rest, drink fluids and dress in light layers. Acetaminophen or ibuprofen can ease discomfort, and aspirin should not be given to children because of the risk of Reye syndrome. Fever is part of the defense against infection and does not always need treatment. Call a doctor for fever in a baby under 3 months, a temperature over 103 F in adults, fever lasting more than 3 days, a stiff neck, severe headache, rash, confusion, trouble breathing or fever in someone with a weak immune system. Febrile seizures affect about 2 to 5 percent of children between 6 months and 5 years.
Based on data from the Mayo Clinic and the American Academy of Pediatrics
