What Causes Chills?

Chills are the shaking, shivering, trembling, and cold feeling you get when your core body temperature drops. Chills can be uncomfortable, but they help raise your core temperature back to a healthy range. When you have chills, your muscles rapidly relax and contract in response to causes like cold temperatures, viruses, or infections.

There are common infections that can cause fevers and chills, as well as side effects from medications, reactions to exercise, hypothyroidism (underactive thryroid), hypoglycemia (low blood sugar), malnutrition (a lack of nutrients), or frisson (a brief thrill). Chills can last a few hours to a few days.

Exposure to Cold

When you get chills without a fever, such as from exposure to cold environments, your brain sends signals to your body to involuntarily move (shake, chatter, tremble) to produce more heat. These chills typically resolve when your body temperature returns to normal. 

You can prevent these chills by dressing for the weather, when possible, by:

• Wearing layers
• Choosing well-insulated but breathable fabrics
• Wearing warm and water-resistant footwear

If you’re experiencing chills at home on a cold day, you can always add layers (sweaters, thicker socks) and get under some blankets with a cup of tea to warm up.

Fever

You can break into a fever after experiencing chills or at the start of an infection. If the fever is mild, 102 F (38.8 C) or less, you can manage it at home by drinking fluids (hydrating and flushing infection) and resting.

Common infections that can cause fever and chills include:

• Gastroenteritis (the stomach flu): Digestive tract inflammation and infectious diarrhea commonly caused by viruses (norovirus in adults and rotavirus in children)
• Influenza: Infections from viruses like influenza A and influenza B
• Sinusitis: A sinus infection, in which the sinuses fill with fluid caused by viruses (less often bacteria)
• Pneumonia: A lung infection caused by many different viruses and bacteria, especially Streptococcus pneumoniae (pneumococcus), and fungi
• Strep throat: A throat infection caused by bacteria known as Group A Streptococcus
• Complicated urinary tract infection: For example, pyelonephritis, a relatively uncommon infection that causes inflammation in the urethra, kidneys, and bladder due to bacteria
• Malaria: A life-threatening infection with cold (chills, shivering) and hot stages (fever) caused by a parasite that is rarely seen in the United States

Side Effects of Medication

Some chills are the result of the body’s response to taking medications and adjusting or stopping medications:

• Diabetes medications: Insulin and drugs like sulfonylureas and meglitinides that increase insulin secretion by the pancreas can cause hypoglycemia-related chills. This happens if you have too much insulin and haven’t matched it with your food intake or physical activity level.
• General anesthesia for surgery: People can experience chills upon waking from anesthesia.
• Chemotherapy medications: Medications that you are taking to calm down your immune system (immunotherapy) and chemotherapy to fight cancer can have flu-like side effects, including fever and chills. Symptoms typically peak and resolve after treatment over a few days.

Reaction to Exercise

There’s a reason it's called warming up and cooling down. When you exercise, your blood circulates to the muscles and skin, raising your temperature. If you stop the physical activity abruptly, your body can experience temperature shock.

Your internal temperature will drop without gradual adjustments, and you may experience chills as a way of warming up to your average temperature again.

Preventing this unpleasant transition means planning a short cool down period to help your body’s temperature adjust to different levels of physical activity.

Hypothyroidism

Hypothyroidism, or underactive thyroid, can result in a low body temperature as a result of insufficient levels of thyroid hormone. A lack of these hormones causes your metabolism to slow. Hypothyroidism causes intolerance to the cold, so you're more likely to experience chills if you have this condition. 

Hypothyroidism risk factors or causes include:

• Thyroiditis (thyroid inflammation)
• Hyperthyroidism (overactive thyroid) treatment, such as radiation or surgical removal
• Iodine deficiency (the thyroid uses iodine to make hormones)
• A family history of thyroid problems
• Being female and over age 60 (or after menopause)
• Postpartum (after giving birth)

Hypothyroidism can be treated with thyroid hormone–stimulating medication. L-thyroxine (levothyroxine) is a commonly used medication.

Hypoglycemia

Chills occur in the mild and moderate stages of hypoglycemia. Hypoglycemia is a condition in which your blood glucose (sugar) is lower than normal, usually under 70 milligrams per deciliter (mg/dL). It can occur in people with diabetes when they continue to take their usual doses of insulin, sulfonylureas, or meglitinides, and they are:

• Not eating enough carbohydrates
• Skipping meals or not eating frequently enough
• Increasing physical activity
• Consuming too much alcohol without eating enough
• Sick with the flu or other illnesses

Nondiabetic hypoglycemia is also possible, but it's much less common.

Treatment of quick-onset hypoglycemia includes raising your blood sugar by consuming glucose (carbohydrates). Frequent episodes should be discussed with a healthcare provider or diabetes specialist.

Malnutrition

Feeling cold all the time or most of the time is a symptom of malnutrition. Malnutrition is when your body is starving for nutrients and cannot function properly. Research suggests that even the lack of one vitamin can lead to malnutrition.

Malnutrition has many causes, including:

• Not consuming enough nutrients
• Not consuming enough food
• Not absorbing the nutrients from food

Without the necessary nutrients it needs, your body cannot maintain a healthy and comfortable body temperature, so you'll experience chills.

If you or a loved one have chills from malnutrition, seek medical attention. Discussing your condition with your healthcare provider, crisis counselor, or a mental health professional may be necessary.

Frisson

Frisson, also known as musical chills or aesthetic chills, is the sensation we tend to call shivering or having goosebumps when experiencing a thrill. Its reaction is similar to that of being cold but without having any exposure to a physical trigger.

Frisson is a short-term, common reaction, and there are many ways of describing the physical response, including:

• Shoulders shuddering or raising to your neck
• Tingly feeling down your shoulders and arms
• Little hairs standing on end
• Trickle down your spine

Summary

Chills could be a result of something benign like experiencing the cold or after exercising, or it could be due to an underlying condition. If you have chills for no obvious reason, check with your healthcare provider to make sure your chills are not caused by an urgent medical issue.

A Word From Verywell

With so many reasons why you could be experiencing chills, it’s always good to make note of when you have them in case you need to discuss your condition with a medical professional. While the odd frisson here and there is nothing to think twice about, if you are experiencing chills for unknown reasons or after starting a new drug or taking an ongoing medication, talk to your healthcare provider. A practitioner can rule out or diagnose underlying thyroid problems, such as hypothyroidism, or blood sugar problems that can be managed. 

If you’re experiencing chills from a fever, try narrowing down the exact cause since different infections, ranging from those caused by viruses or bacteria or parasites, are treated with different medications. If your fever isn’t improving with medication, rest, and plenty of fluids or if you have a very high fever, call your healthcare provider.