Chills: What Causes Them and When to Worry

Symptoms of a chill

A chill usually includes:

• feeling cold, often suddenly, even under blankets
• shivering or trembling of the muscles
• goosebumps
• teeth chattering
• pale, cool hands and feet as blood vessels in the skin narrow
• wanting to curl up and add layers

Doctors grade chills by intensity:

Rigors are linked more strongly with bacteria in the bloodstream than milder chills, so they deserve more attention.

Why chills happen

The hypothalamus, the brain's thermostat, normally keeps body temperature near 37 °C (98.6 °F). During an infection, immune chemicals called pyrogens reset the thermostat higher. Your body now feels "too cold" compared with the new setting, so it:

• narrows blood vessels in the skin to conserve heat
• makes muscles shiver, which produces heat quickly

Once the temperature reaches the new set point, chills stop and you feel hot. When the fever breaks, the process reverses: you sweat and feel flushed. That is why chills come before a fever spike and sweats come after.

What chills can be a symptom of

Infections (most common)

• Viral infections: flu, COVID-19, colds, gastroenteritis and mononucleosis.
• Pneumonia: a single shaking chill at the start, followed by cough, fever and chest pain, is classic for pneumococcal pneumonia.
• Urinary tract and kidney infections: chills with burning urination and back or flank pain point to pyelonephritis.
• Skin infections: cellulitis and abscesses.
• Strep throat and sinus infections.
• Malaria: cycles of shaking chills, high fever and sweats after travel to an affected area.
• Bloodstream infections and sepsis: rigors with feeling very unwell.
• Endocarditis, abscesses and bone infections: recurrent chills and fevers without an obvious source.
• Tick-borne and other infections: Lyme disease, ehrlichiosis, brucellosis and tuberculosis.

Non-infectious causes with fever

• reactions to blood transfusions, vaccines or IV medicines
• autoimmune and inflammatory conditions
• some cancers, especially lymphoma, which can cause fevers, chills and drenching night sweats
• drug fever

Chills without fever

• Cold exposure and wet clothing, or hypothermia
• Low blood sugar (hypoglycemia): shaking, sweating, hunger and confusion, especially in people on insulin or sulfonylureas
• Hypothyroidism: constantly feeling cold, tiredness, weight gain, constipation
• Anemia: feeling cold with tiredness and breathlessness
• Anxiety and panic attacks: trembling and chills from an adrenaline surge
• After anesthesia: shivering is common on waking
• Intense exercise in the cold, or after a marathon
• Alcohol or opioid withdrawal
• Low body weight and malnutrition

Accompanying symptoms and what they suggest

How doctors find the cause

A doctor will ask when the chills started, how severe they are, your temperature readings, other symptoms, recent travel, surgery, procedures, medicines and immune status. Examination focuses on the chest, urine, skin, throat, abdomen, heart murmurs and lymph nodes.

Tests depend on the picture:

• blood count and inflammatory markers
• urine test and culture
• blood cultures, especially with rigors
• chest X-ray
• flu, COVID-19 or strep tests
• malaria blood films after travel
• thyroid function and blood sugar for chills without fever

Treatment and home care

The cause determines treatment. Antibiotics are used only for bacterial infections. While a viral illness runs its course:

• Rest and fluids. Fever and shivering increase fluid loss.
• Fever reducers: acetaminophen (paracetamol) or ibuprofen, following the label dose, ease chills and aches. Do not give aspirin to children or teenagers.
• Dress in light layers and use one blanket. Piling on heavy covers during chills can push the temperature higher once the fever peaks. Remove layers when you start to feel hot.
• Avoid cold baths, ice or alcohol rubs, which cause more shivering.
• Check your temperature every few hours and note when chills occur.

If you have diabetes and feel shaky and chilled, check your blood sugar first and treat a low reading with fast-acting sugar.

Frequently asked questions

What can chills be a symptom of?

Chills are most often a symptom of an infection, such as flu, COVID-19, a cold, pneumonia or a urinary tract or kidney infection. They can also come from cold exposure, low blood sugar, an underactive thyroid, anemia, anxiety, medicine reactions and, less often, sepsis, malaria or lymphoma.

What are the symptoms of a chill?

A chill involves feeling cold, shivering, goosebumps, chattering teeth and pale, cold hands and feet. It often comes just before or as a fever rises. Severe chills, called rigors, cause uncontrollable whole-body shaking for several minutes.

Can you have chills without a fever?

Yes. Chills without fever can come from cold or wet conditions, low blood sugar, anxiety, an underactive thyroid, anemia, hunger, intense exercise or the early phase of an infection before the temperature rises. Recheck your temperature an hour later.

Are shaking chills serious?

Shaking chills, or rigors, are more often linked with bacterial infections in the blood than ordinary chills. With a high fever, confusion, fast breathing or feeling very unwell, they need urgent medical assessment because they can signal sepsis.

Should I cover up or stay cool when I have chills?

Use a light blanket or layer to stay comfortable while shivering, then remove it as soon as you feel hot. Heavy bundling can drive a fever higher. Drink fluids and take a fever reducer if needed.