7 Conditions That Might Cause Chills With No Fever
Why Do I Feel Chills, but No Fever?
A fever is an abnormally high body temperature. A normal body temperature usually ranges from 36.5oC to 37.2oC, or 97.8oF to 99oF. A person with a fever experiences a temperature spike, often starting from 37.2oC or 99oF.
While a fever is technically not an illness, it is often a symptom of one, usually an infection. In order to counteract the infection, the hypothalamus in the brain sends signals to raise the body’s temperature.1 When the rest of the body detects this heat increase, it starts working overtime to regulate its new, higher temp. This often leads to chills which can be experienced as sudden, uncontrollable tremors all over the body.
Though usually chills are accompanied by a fever, that's not always the case. There are medical conditions which may manifest as chills without a fever. These may include the following, which are all described in detail below.
- Cystitis or infection of the bladder
- Complications with prescription medicine
- Anemia or low hemoglobin
- Hypoglycemia or low glucose / blood sugar
- Lack of sleep
- Cold environment
7 Possible Causes of Chills Without a Fever
Cystitis or infection of the bladder
Increased urination, sensation of a full bladder even when you just emptied it, strong-smelling, cloudy, or bloody urine, cramping in abdomen, burning sensation during urination
Depression, exhaustion, lightheadedness, weight loss
Increasing nutritional content or variety of diet
Anemia or low hemoglobin
Cold hands and feet, weakness and fatigue, pale skin, depression, angina (severe chest pain), dizziness and/or difficult or labored breathing, a fast or irregular heartbeat, cognitive difficulties, headaches
Depends on type of anemia; for iron-deficiency anemia, iron intake should be increased
Depression, shakiness, jitteriness, vision problems, confusion or delirium, heart palpitations, anxiousness, weakness or trembling, sweating, intense hunger
Immediate ingestion of 15 grams of carbohydrates
Depression, fatigue, weakness, or listlessness, constipation, heavy menstrual period, aching joints and muscles, pale skin, weight gain, fragile or thin hair or fingernails that break easily
Taking synthetic thyroid hormone
Lack of sleep
Sleepiness, irritability, weight gain, yawning, depression, moodiness
Get more sleep
Frostbite, hypothermia, shivering, hunger, nausea, fatigue
Wear warm clothing, avoid excessively cold environments
What Are Chills?
Chills occur when the body attempts to produce heat to increase its temperature from within, causing muscles to contract and relax rapidly.2 You can see goosebumps on the skin when it is cold and during times of stress. Goosebumps also occur when chills manifest.
Signs of Chills
Chills can come and go or remain constant.2
- Chattering teeth - When you experience a drop in temperature, your hypothalamus sends a signal to the rest of the body to generate more heat. Shivering is a form of muscle contraction that allows the body to produce heat. Chattering teeth often accompany chills.
- Goosebumps - While goose bumps are not a symptom of chills, these often appear when an individual feels cold.
- Sweating - When your body tries to generate more heat in cold environments, your warmer spots (e.g., armpits) begin to produce more sweat. The cold temperature may also cause moisture to evaporate slower, which can make your skin feel clammy and sweaty.
- Shivering or shaking - This is caused by the contractions of your muscles.
Causes for Chills Without a Fever
Chills could happen simply because of exposure to cold weather, but it could also indicate a bacterial or viral infection in the body. If the chills occur without a fever, it may indicate any of the following conditions:
1. Cystitis or Infection of the Bladder
Bladder infections (aka cystitis or urinary tract infections) affect women much more than men. Most of these infections are caused by bacteria that enter the urethra and then the bladder and can spread to the kidneys if left unchecked.3
One in five women will get a bladder infection at some point in her life. If she's had one before, she's more likely to have another. Men rarely get bladder infections, although the likelihood he will increases with age.
Its symptoms may include:3
- Chills (with or without a low grade fever) - When you begin to experience fever and shivers with urinary tract infection, this may mean that the infection has reached your kidneys. This does not happen with every case of cystitis but if it does, seek professional health immediately.
- Increased urinary frequency - Individuals with a bladder infection feel the need to urinate more often than normal people. Studies show that infected individuals might make up to sixty trips to the bathroom per day. However, these frequent bathroom visits often result in smaller amounts of urine than what healthy people make.
- The sensation of a full bladder even when you just emptied it - Cystitis makes a person think that she is always carrying a full bladder, even if she has just finished urinating. This causes a constant and urgent need to pee, even when the bladder does not actually contain any fluid yet. However, if the infected person is unable to urinate immediately, she may experience abdominal pain in varying degrees.
- Strong-smelling, cloudy, or bloody urine - About 10 percent of women with a bladder infection have bloody urine. This happens because the kidney allows red blood cells to enter into the pee. This condition is called hematuria, and is linked not just with urinary tract infections, but also with kidney stones and other kidney infections. On the other hand, cloudy and strong-smelling urine may be symptoms not only of cystitis, but also of dehydration, an autoimmune disorder, or other kidney or bladder infections.
- Cramping in abdomen - A bladder infection can be very painful, especially in the abdominal or urethral area. This happens because the bladder becomes inflamed, which causes your abdomen to feel pulsing pain and cramps. You can also feel like there is pressure in the lower abdomen.
- A burning sensation during urination - Because of the inflamed bladder and urethra, it is hard, sometimes even painful, for a person with cystitis to urinate.
If you experience any or all of these symptoms, you should consult a physician to determine the underlying cause. If it is a urinary tract infection, your doctor may prescribe antibiotics such as ampicillin, penicillin, or sulfisoxazole.
The duration of treatment depends on the age and gender of the patient but lasts three days for most women. Male patients and children require longer duration of treatment, usually from seven to ten days. In some cases, the infection spreads to the kidneys or the patient may need to undergo a surgical procedure to address any problems that may have caused the infection.
If you've had cystitis before and then have a mild relapse after a few months, you can try treating your symptoms at home. Though these preventative self-care measures are not well-studied, some doctors recommend the following:3
- Drink lots of water and take ibuprofen or paracetamol to ease the pain.
- Try a hot compress by placing a bottle of hot water or a warm cloth on your stomach.
- Try to abstain from any sexual intercourse for a few days, since bacteria can pass through your urethra during sex.
- If your symptoms persist after a week, check in with your doctor to see if you need a higher dose of medication.
If you are prone to getting urinary tract infections, you can try the following measures to prevent it from coming back:3
- Drink plenty of water and other fluids. Staying hydrated prevents bacteria from spreading in your bladder and urethra.
- Empty your bladder as soon and as often as you can. Keeping in your urine stresses your bladder, and causes bacteria to inhabit it for longer periods. By regularly urinating, you wash out the toxins in your body and help keep your bladder healthy.
- Do not use products with strong chemical ingredients on or around your genitals. These include talcum powder and strong, perfumed soaps. Opt for the plain, unscented variety instead.
- Wipe your bottom from front to back after using the toilet, to keep bacteria from entering your urethra.
- Wear comfortable underwear made of cotton to allow your genitals to breathe. Avoid wearing tight-fitting clothes regularly as doing so stresses your genitals.
- Urinate as soon as possible after you have sexual intercourse to help flush out the bacteria.
Malnutrition is one of the leading causes of common diseases. When the body does not get enough nutrients, it becomes vulnerable to viruses and bacteria, and it lacks the energy it requires to perform even the most basic tasks.
There are numerous reasons the body might not get adequate nutrients. These include digestion and absorption issues, insufficient food or food that lacks proper nutrition, and secondary health conditions.
Though the symptoms will vary depending on what kind of nutrient is deficient, general signs of malnutrition can include:4
- Chills without fever - Malnourished individuals often lack proper body heat because they do not have enough stored fat in their bodies. Less fat means less heat, so the malnourished person may feel cold even when he does not have a fever. This may cause chills and shivers, and even light tingles in the extremities.
- Depression - Micronutrient deficiency can cause behavioral changes, the most common of which is depression. A malnourished person may also experience bouts of uncontrollable irritation, anxiety, and the lack of interest in social interactions.
- Exhaustion - When the body does not have enough nutrients, it doesn’t have the energy it needs to perform certain tasks. This causes a perpetual feeling of fatigue and inability to remain energetic throughout the day.
- Lightheadedness - Malnutrition affects brain functions, so a malnourished person can end up lightheaded and unable to concentrate for long periods of time.
- Weight loss - Weight loss is perhaps the most obvious symptom of malnutrition. A malnourished individual often has less appetite than the normal person, which means he is likely to end up getting fewer nutrients in his body. When the body does not get all the necessary nutrients it needs, the muscles atrophy, and the body burns its stored fat quicker in an effort to survive.
The symptoms of malnutrition may come and go depending on the cause of malnutrition. A doctor will assess the situation and make a prescription, depending on the circumstances.
Preventing micronutrient deficiency may sound easy, yet a lot of people find themselves malnourished for different reasons. To avoid malnutrition, make sure you do the following:
- Maintain a healthy, balanced diet. Your meals should ideally contain proteins (e.g., meat, chicken, fish, eggs), carbohydrates (e.g., rice, bread, pasta), dairy (e.g., milk, cheese), and fruits and vegetables. Eating a wide range of vegetable of all different colors will help you make sure you get the nutrients you need.
- Avoid junk food, processed foods, and food rich in preservatives, as these are harmful to your body.
- You might consider taking vitamins and other dietary supplements. There are many over-the-counter supplements that can replace the nutrients you do not get from your food. However, you should be sure you understand the health benefits and risks of these supplements before taking them. Consult your doctor to find out which supplement is best for you.
3. Anemia or Low Hemoglobin
Anemia is a common blood condition, especially in women and young children. At least 3.5 million Americans are reported to be suffering from this condition, even when they appear to be fit and healthy.
Anemia is a deficiency of red blood cells or hemoglobin in the blood. Its symptoms include:5
- Cold hands and feet - When small blood vessels in your extremities receive too little iron, they become more susceptible to drops in temperature, which is why a lot of anemic individuals have freezing hands and feet.
- Weakness and fatigue - Iron deficiency causes an individual to feel constantly tired, weak, and lethargic because the muscles are not getting the right amount of oxygen they need to function properly.
- Pale skin - Anemic people often have an unusually light skin color, because of the low amount of red blood cells that flow through their bloodstream.
- Depression - Anemia is sometimes connected with clinical depression, and can even slow down the recovery of substance abusers.
- Angina (severe chest pain) - Low hemoglobin levels forces the heart to work double time to supply the required amount of oxygen and blood to the rest of the body. When the heart becomes overworked, a person can suffer from severe chest pains or other heart diseases, including a full-blown heart attack.
- Dizziness and/or difficult or labored breathing - Anemia can cause lightheadedness and vertigo, because the heart is having a hard time delivering enough oxygen to the brain. Also, when the body has low levels of oxygen, a person can experience erratic, labored breathing.
- A fast or irregular heartbeat - Iron deficiency causes palpitations because the heart needs to work extra hard to circulate blood to the body. While an irregular heartbeat is not a definite symptom of heart failure, it is still advisable to consult with a doctor if it occurs frequently.
- Cognitive difficulties - People with low levels of iron in their bloodstream find it hard to concentrate on mental activities. They also have difficulties remaining motivated to do tasks.
- Headaches - An iron deficiency in the brain causes brain arteries to swell, which could lead into a headache.
The cause of anemia determines how it will be treated. If an iron or nutrition deficiency is the cause, doctors may give supplements to be added to the patient’s daily dietary regimen. If it is caused by severe loss of blood, treatment may involve a blood transfusion.
If it is an autoimmune condition, the physician may prescribe drugs to keep the immune system in check. Bone marrow problems may also cause anemia. This is managed with erythropoietin, a medication that acts to stimulate production of blood cells in the bone marrow.
While many types of anemia cannot be prevented, you can avoid iron-deficiency anemia by doing the following:6
- Eat iron-rich food, including red meat, seafood, beans, and green, leafy vegetables.
- Eat foods rich in folate, B-12, and Vitamin C
- Avoid drinking too much coffee, black tea, and other caffeinated products, as these contribute to slower iron absorption.
- Take an iron supplement, especially if you are a vegan or vegetarian. Consult your doctor on what kind of supplement you can take regularly.
4. Hypoglycemia or Low Glucose/Blood Sugar
Hypoglycemia is a clinical syndrome that results from low blood sugar in people with diabetes and occasionally (but not frequently) in other people. Its symptoms come on quickly and can include:7
- Chills without fever, shakiness, or jitteriness - Glucose is an important source of energy for your cells. When your body does not have enough glucose, your central nervous system may malfunction and release a chemical called catecholamine to help your body produce more blood sugar. A sudden rush of catecholamine in your body can cause uncontrollable shakes and tremors.
- Vision problems - Low blood sugar may cause blurry or double vision because the central nervous system is not getting enough sugar for it to work properly.
- Confusion or delirium - The brain becomes very sensitive when it lacks glucose, so you may end up becoming confused or unable to focus on an activity.
- Heart palpitations - Insufficient levels of glucose can cause palpitations and erratic heartbeats or the feeling that you will suffer from a heart attack.
- Anxiousness - Low glucose levels cause the adrenal glands to produce epinephrine, a hormone that signals the liver to create more sugar. This induces an adrenaline rush, which is often followed by a bout of sudden anxiety.
- Weakness and/or trembling - A drop in blood sugar may cause you to feel weak, and even faint. This may be accompanied with shakes and tremors, too.
- Diaphoresis (sweating) - Excessive sweating is usually one of the first symptoms of low blood sugar. When the body’s glucose levels drop, the autonomic nervous system prompts the skin to secrete excess moisture.
- Intense hunger (perhaps to the point of nausea) - When your body lacks glucose, your brain will signal you to eat more, even when you have just finished eating. When you give in to these sudden cravings, your digestive system has the tendency to overload, which may cause nausea and vomiting.
When hypoglycemia is the problem, intervention involves an immediate increase of blood sugar via intake of food with high sugar content. As soon as blood sugar levels have normalized, the next step is to determine what caused the patient to become hypoglycemic.
Some causes include uncontrolled diabetes, excessive alcohol intake, side effect of medication, high levels of insulin, endocrine problems, and kidney or liver conditions. Once the underlying cause is determined, appropriate treatment can be rendered.
Diabetic people have maintenance medication and insulin and work with their healthcare team to moderate their blood sugar levels. It is rare to experience hypoglycemia if you are not diabetic. If you do, however, try to follow these steps to control your glucose levels:7
- Eat food rich in carbohydrates, especially if you plan to exercise or do a strenuous activity.
- Carry a snack with you at all times and try to eat small meals every two hours to maintain your levels of glucose in your blood.
- Avoid drinking too much alcohol, as this affects the ability of your body to release glucose in the bloodstream.
- Monitor your glucose levels. This is especially important if you have a family history of diabetes, or were tagged as prone to hypoglycemia by your physician.
- Seek a doctor to find the underlying cause of your hypoglycemia.
The thyroid is a gland that releases metabolic hormones. Hypothyroidism occurs when the gland is under active and does not generate adequate hormones to control the way your body uses energy. Its earliest symptoms may include:8
- Chills without fever or increased sensitivity to cold - An under active thyroid means your cells do not use up much energy. When this happens, your body produces less heat, which leads to chills. You may notice that you are not as able to handle cold temperatures as those around you.
- Depression - Thyroid hormones are connected to the production of serotonin, which is the hormone in the brain that causes feelings of happiness. When your brain produces too little serotonin, you will begin to feel down for no apparent reason.
- Fatigue, weakness, or listlessness - Feeling tired is normal when you just finish a strenuous activity, but if you still feel weak after a good night’s sleep or a whole day of rest, you may be suffering from hypothyroidism. This happens when there is too little thyroid hormone in your bloodstream, so your muscles feel exhausted even when you’re supposed to be well rested.
- Constipation - Many people with low thyroid hormone levels experience problems in bowel movement, because of a slowdown in their digestive system.
- Heavy or abnormal menstrual period - A short supply of thyroid hormones cause heavier and more painful menstruation.
- Aching joints and muscles - Muscles pain and aches in your extremities may be caused by hypothyroidism. Your hands and feet, and even your joints, may also experience erratic tingles and pain.
- Pale skin - Hypothyroidism can cause pale, dry, and flaky skin because the body cannot produce enough moisture to keep your skin hydrated.
- Weight gain - A sudden gain in weight is one of the most common symptoms of an under active thyroid, because the body’s metabolism slows down and fails to burn excess stored fat.
- Fragile or thin hair or fingernails that break easily - Low levels of thyroid hormone cause hair loss, because too many follicles stop functioning properly. Similarly, fingernails and toenails become brittle, stiff, and prone to ridges.
As the condition develops, other symptoms become apparent such as bloating in the face, feet, and hands, slow or hoarse speech, thickening of the skin and thinning eyebrows, and loss of taste and smell.
When your thyroid is sluggish, you'll need to take hormones to replenish the deficiency. Medical management may involve Levothyroxine that the patient must sometimes continue taking even after symptoms are gone.
In many cases (such as surgical removal of the thyroid gland), hypothyroidism cannot be prevented. There are a few things that you can do to prevent other causes of hypothyroidism, such as:9
- Quit smoking. Cigarettes contain harmful chemicals that may damage your thyroid, or complicate an already existing thyroid condition.
- Avoid taking too much soy or soy-rich products. While soy is good for your health, eating too much can trigger a thyroid disease as well as affect your immune system.
- When getting a chest X-ray, request for a thyroid collar to prevent your thyroid from getting exposed to unnecessary radiation. While this may sound finicky, it is a good step to decrease your chances of thyroid-related problems.
- Have regular checkups. If you experience any of these symptoms, visit your doctor and have your thyroid levels tested, to see if you are suffering from hypothyroidism.
6. Lack of Sleep or Insomnia
The average adult needs seven to eight hours of sleep every day. If you are getting less sleep than this, your body becomes more prone to illness and other health risks. Aside from serious health problems like type 2 diabetes and heart failure, lack of sleep can cause the following:10
- Chills without fever - Your body temperature drops while you sleep. So when you don’t get enough of it, you start shivering because your body is trying to lower your temperature while you are awake.11
- Weight gain - When you don’t get enough sleep, your metabolism slows down, and your appetite increases. It doesn’t help that sleep deprivation also causes you to crave high-carb and high-fat foods. This combination is a guaranteed recipe for weight gain.
- Shifting moods - Insomnia is often connected to depression, and people who sleep less tend to become more emotional. This is because “happy” hormones, such as serotonin, often replenish during sleep, so the fewer hours you stay in bed, the less of them you produce.
- Swollen eyes and dark under-eye circles - Tired, puffy eyes are a common effect of sleep deprivation. This is because your body loses moisture when you are awake, and too little sleep can eventually lead to skin dehydration.
- Higher stress levels - Stress-regulating genes are often sent to disarray when your body gets fewer than eight hours of sleep. When this happens, you will start to feel more anxious, irritated, or stressed over the smallest things.
- Slower brain functions - Sleep deprivation causes the brain to function slower, and affects its ability to remember new information. Not only will this cause you to have a harder time learning new things, it can also lead you to poor decision-making.
- Poor immune system - Antibodies often replenish during sleep, so when you don’t get enough of it, this makes you more vulnerable to infections and different types of illness.
There are many remedies to help you fall asleep easily and deeply. For example, drinking a cup of hot chamomile tea before bedtime helps relax your body and prepares you for sleep. The right room temperature also helps you sleep faster. There are also over-the-counter sleeping aids and supplements available in pharmacies. Make sure to consult with your physician before buying any type of sleeping pills, to help you understand its benefits and side effects.
Here are other ways to prevent insomnia:
- Avoid stimulants, especially at night. These include caffeinated drinks and nicotine products. Drinking alcohol, while helpful in falling asleep, causes restlessness, and increases your chances of waking up in the middle of the night.
- Exercise regularly. Studies show that regular exercise can help you sleep faster, longer, and more soundly. But avoid exercising before bedtime, as this will stimulate your body and keep you awake longer than you wish.
- Keep your bed comfortable and your room temperature cool (but not freezing). The more relaxed you feel before bedtime, the quicker you can fall asleep.
- Avoid long, frequent naps during daytime, as this will affect your sleeping pattern. Your body will also have a hard time slowing down when it has excess energy from your nap.
- Stay relaxed and avoid getting stressed before going to bed. Try meditation, deep breathing, and other techniques to relax your body and mind before sleeping.
7. A Cold Environment
Sometimes, chills happen because of the most obvious reason: The temperature is cold. However, while shivering is a normal response to cold weather, excessive cold can be bad for your health. Too much exposure to cold may cause the following:
- Chills without fever - When your body is exposed to a cold climate, it will try to raise its internal temperature by coaxing your muscles to produce more heat. One way to do that is by shivering.
- Hypothermia - Hypothermia happens when the body fails to adjust to the loss of heat in extreme environments. When this happens, the affected person begins to lose sensation in his extremities, which is then followed by the weakening of muscles, drowsiness, and diminished consciousness.12
- Frostbite - Frostbite is one of the most common effects of prolonged exposure to freezing temperature. When this happens, blood circulation stops in the affected tissue, causing it to become inflamed, or worse, go numb and turn into a bluish or purplish hue.13
- Immersion foot - This medical condition happens when your feet have mostly remained wet for days. Because the feet soaks up so much water, their nerves and muscle tissue begin to grow numb. Individuals with immersion feet might also experience itching and tingling, and gangrene might develop if proper medication is not applied immediately.14
- Chilblain - These are painful, itching swellings that occur on the skin and are usually found on the hands or feet. While not as grave as other symptoms, chilblains can still be painful, especially when the skin begins to swell and blister. Body parts that are usually affected are the nose, earlobes, fingers, and toes.15
Staying Safe in Cold Weather
While it is ideal to just stay indoors and bundle up when the weather is chilly, real life often requires you to leave the house even in cold weather. Here are some tips to help you keep warm:
- Wear multiple layers of clothes to stay warm outdoors. Protect your hands and feet with thick gloves and socks, and a pair of waterproof, insulated shoes. Consider wearing a cap, bonnet, or hoodie, especially if the weather is damp. Ear muffs are also helpful, especially when it is snowing.
- Take plenty of water to keep yourself hydrated. This will help boost your immune system and make you more resilient against flu and cold viruses. Vitamin C supplements are also helpful to strengthen your immune system.
- When you experience frostbite, do not rub or massage the affected area. Instead, use a hot compress or heating pad to raise its temperature. Stay near a source of heat, like a fireplace or radiator, or even a cooking stove, to lessen the effects of frostbite and return your body temperature to normal.
Other Causes for Chills Without Fever
What if you're perfectly healthy but you still feel cold? If there is no underlying health problem causing the chills, they might be managed through certain natural solutions or remedies.
- Adequate rest and enough hours of sleep without disturbance can alleviate chills. The recommended number is eight to nine hours of continuous, uninterrupted sleep.
- Consume sufficient amounts of nutritious food without skipping meals. Make sure to keep healthy foods on hand in case hunger strikes, like fruit, energy bars, or other handy snacks.
- Maintain a regular exercise regimen. It does not have to be rigorous. Morning walks or doing laps in the pool are recommended. Physical activity is great for keeping your blood circulating.
- Vitamin B is highly beneficial to maintain homeostasis in the body. This vitamin can help alleviate chills and improve energy.
- Taking sips of warm water is very relaxing for the body, aids in digestion, and reduces chills. It helps to keep the body hydrated and also helps maintain body heat.
- Drinking hot herbal tea with honey or eating warm chicken soup is good for the stomach and can help reduce chills. It also helps hydrate the body.
- A warm bath or shower can soothe and provide warmth to the body and reduce chills.
- Thick, comfortable clothing can help keep the body warm, especially in a cold environment. When going outdoors in freezing weather, wear thermal clothes to lock in your body heat.
- Mayo Clinic Staff. "Fever." May 29, 2014. Mayo Clinic. Accessed May 1, 2017.
- Donohue, Maureen, and Valenica Higuera. Medically Reviewed by Steven Kim, MD. "What Causes Chills? 77 Possible Conditions." October 1, 2015. Healthline. Accessed May 1, 2017.
- Mayo Clinic Staff. "Cystitis." March 18, 2015. Mayo Clinic. Accessed May 1, 2017.
- Healthline Editorial Team. "Nutritional Deficiencies (Malnutrition)." November 6, 2015. Healthline. Accessed May 1, 2017.
- Reviewed by Melinda Ratini, DO, MS. "Understanding Anemia -- Symptoms." March 4, 2015. WebMD. Accessed May 1, 2017.
- Mayo Clinic Staff. "Anemia: Self-Management." August 6, 2016. Mayo Clinic. Accessed May 1, 2017.
- Brusie, Chaunie RN, BSN. Medically Reviewed by Tyler Walker, MD. "Can You Have Hypoglycemia Without Having Diabetes?" April 25, 2016. Healthline. Accessed May 1, 2017.
- Reviewed by William Blahd, MD. "Hypothyroidism (Underactive Thyroid)." August 13, 2015. WebMD. Accessed May 1, 2017.
- Shomon, Mary. "Things You Can Do to Prevent a Thyroid Condition." February 25, 2017. VeryWell. Accessed May 1, 2017.
- Pietrangelo, Ann. Medically Reviewed by George Krucik, MD, MBA. "The Effects of Sleep Deprivation on the Body." August 19, 2014. Healthline. Accessed May 1, 2017.
- Bianchi, Jane. "The 10 Weirdest Side Effects of Sleep Deprivation." June 10, 2013. Woman's Day. Accessed May 1, 2017.
- Mayo Clinic Staff. "Hypothermia." June 18, 2014. Mayo Clinic. Accessed May 1, 2017.
- Mayo Clinic Staff. "Frostbite." October 15, 2014. Mayo Clinic. Accessed May 1, 2017.
- "Trench Foot or Immersion Foot." (n.d.) CDC. Accessed May 1, 2017.
- Mayo Clinic Staff. "Chilblains." December 10, 2015. Mayo Clinic. Accessed May 1, 2017.