Knowledge
Sourced guides on how the body stays warm, how patients and clinicians are kept comfortable, how crews work safely in cold and heat, and how warming gear works. Pick the theme closest to your world.
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Science of Warmth
For anyone who wants to understand how the body makes, keeps and loses heat.
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Healthcare
For clinicians, perioperative teams, hospital leaders, and patients before and after surgery.
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- Patient warming and perioperative hypothermia
- Thermal comfort for clinicians
- For patients: surgery and recovery
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- How to stay warm in the operating room
- What is perioperative hypothermia?
- Forced-air vs conductive warming
Work and Duty
For employers, safety leads, crews, service members and EMS.
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Everyday Life and Health
For people who feel the cold, and for daily life outdoors.
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- Cold sensitivity and Raynaud’s
- Staying warm in everyday life
- Staying warm at home and with family
- Staying warm with a health condition or disability
- Medications and feeling cold
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Heat and Cooling
For hot jobs, heavy protective gear and personal heat sensitivity.
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Technology and Gear
For choosing, using and caring for warming gear.
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Heated scrub jackets and warm OR layers: a buyer's guide
Before buying a heated scrub jacket, check five things: whether your facility's attire policy allows a personal or battery-powered layer in your area, where the battery and cord sit, whether the garment can be laundered the way policy requires, whether it fits under a gown or lead apron, and whether a passive heat-reflective or insulated layer would do the job with fewer approvals.
Hypothermia blankets compared: HPMK, Blizzard, Ready-Heat and space blankets
Active systems that add heat, such as the HPMK and Ready-Heat blankets, generally lost the least heat in fluid-model lab studies, and the Blizzard insulated blanket was the best passive option in the Army and UK studies. Plain space blankets and single wool blankets ranked lowest. The military Joint Trauma System recommends an insulated wrap plus an active heat source, kept off bare skin.
Why batteries die in the cold: phones, vapes, e-bikes and heated gear
Batteries die in the cold because low temperatures slow the chemistry inside lithium-ion cells. The electrolyte thickens, internal resistance rises, and the cell cannot deliver power fast enough, so devices drain quickly or shut off. Apple and Samsung design their phones for 32 to 95 °F (0 to 35 °C). The loss is usually temporary and returns once the battery warms.
Hand warmers for Raynaud's: what helps and what to avoid
The best hand warmers for Raynaud's give gentle, steady heat you can start before your fingers get cold: rechargeable warmers with adjustable settings, air-activated packets inside mittens, or click warmers for a quick boost. The National Institutes of Health lists hand warmers and heated gloves among Raynaud's self-care steps. Pair them with a warm core, and never press a hot warmer against numb skin.
Toe warmers, body warmers and insoles: which warmer goes where
Disposable toe warmers are rated to last up to 7 to 8 hours, and stick-on body warmers up to 12 to 18 hours. Toe warmers are built to run cooler, around 102 to 113 °F (39 to 45 °C), because they sit inside a boot against the foot. Each type is shaped for one place, so match the warmer to the spot.
Rechargeable vs disposable hand warmers: which is better?
Neither wins everywhere. Disposable air-activated warmers run longer per use, often rated at up to 10 hours, need no charging and suit occasional use. Rechargeable warmers are often rated for up to about 6 hours per charge on low, offer adjustable heat and cost less over many uses, but they carry lithium-ion battery risks and follow FAA battery rules when you fly.
Reusable click hand warmers (sodium acetate): how they work
Reusable click hand warmers hold a supersaturated solution of sodium acetate in water. Flexing the small metal disc starts crystallization, and as the liquid turns solid it releases stored heat, reaching about 129 °F (54 °C). The heat lasts minutes rather than hours. Boiling the pad in water redissolves the crystals so it is ready to use again.
Can you reuse a disposable hand warmer?
Not fully. A disposable air-activated hand warmer cannot be recharged once its iron has oxidized, but you can pause a partly used one. Seal it in an airtight zip-top or freezer bag with the air pressed out, and the reaction slows to a stop. Open the bag later and it heats again, using only the energy that was left.
Where to put hand warmers on your body to stay warmest
Put warmers in two places: on your core and where you feel cold. An adhesive body warmer stuck to your base layer over the upper back or chest keeps blood flowing to your hands, while hand warmers go in mittens, glove pockets or jacket pockets. In a Canadian defense research study at -13 °F (-25 °C), heating the torso kept fingers more dexterous than heating the hands directly.
Medications that can make you feel cold: a reference list
Several medicine classes can make you feel cold. Beta blockers, ADHD stimulants, triptans and ergot drugs can narrow blood flow to the fingers and toes; oxaliplatin causes nerve symptoms triggered by cold; and antipsychotics can occasionally lower core body temperature. A 2016 review identified 12 drug classes linked to Raynaud's phenomenon. Never stop a medicine on your own; talk to your prescriber first.
Hypothyroidism and feeling cold: a deeper guide
Hypothyroidism makes you feel cold because low thyroid hormone slows the body's metabolism, so it produces less heat at rest and less extra heat when you are chilled. In a Swiss study, restoring normal thyroid levels raised the body's heat response to mild cold by about 102%. Most people warm up with proper treatment, but persistent cold deserves a talk with your clinician.
ADHD stimulants and cold hands
Yes, ADHD stimulants can cause cold hands. US labels for amphetamine (Adderall XR) and methylphenidate (Concerta) warn that these medicines are associated with peripheral vasculopathy, including Raynaud's phenomenon: fingers or toes that feel numb, cool or painful and turn pale, blue, then red. Symptoms are usually mild and intermittent. Tell the prescriber, and do not change the dose on your own.
Beta blockers and cold hands and feet
Yes. Cold hands and feet are a recognized side effect of beta blockers. The NHS lists them among common side effects, and US labels for metoprolol and propranolol list cold extremities or arterial insufficiency of the Raynaud type. Beta blockers lower the heart's output and can block signals that widen small blood vessels. Never stop one suddenly; talk to your prescriber.
Feeling cold on Mounjaro or Zepbound (tirzepatide)
Feeling cold is not a listed side effect of Zepbound or Mounjaro. Neither US prescribing information lists chills, feeling cold or cold intolerance. The likely reasons are indirect: tirzepatide decreases calorie intake, and weight lost is mostly fat, which insulates. Listed effects such as fatigue, dizziness and low blood pressure can also feel like a chill. Persistent cold deserves a talk with your clinician.
Why losing weight makes you feel colder
Losing weight can make you feel colder because you have less body fat to insulate you and because eating less turns down heat production. In a six-month JAMA trial, people on calorie restriction had lower core body temperature and burned about 135 fewer calories a day while sedentary. Cold that is extreme, long-lasting or comes with unplanned weight loss deserves a clinician's check.
Shivering after a C-section or childbirth
Shivering after a C-section or childbirth is very common and usually harmless. Research reviews report that up to 85% of people shiver after spinal anesthesia for a cesarean, and many shake after a vaginal birth too. It usually settles within an hour or two with blankets and warming. Shaking with a fever of 100.4 °F (38 °C) or heavy bleeding needs prompt attention.
Feeling cold during and after a blood transfusion
Feeling cold during a blood transfusion can come from the blood itself, since red cells are refrigerated at about 43 °F (6 °C), or from a reaction. Chills with a fever are one of the most common reactions, occurring in about 1% of transfusions. Because chills can also signal a rarer, serious reaction, tell your nurse the moment you feel chilled or shaky.
Why hospital rooms feel cold: patient rooms, the ER and imaging
Hospitals feel cold mostly because of the person, not the thermostat. CDC infection-control guidance lists a design range of 70 to 75 °F (21 to 24 °C) for patient rooms, an ordinary indoor range. Patients feel colder because they lie still in a thin gown, may be ill or fasting, and may receive room-temperature IV fluids. Imaging and equipment rooms can run cooler.
Staying warm while recovering at home after surgery
Feeling cold for weeks after surgery is common and usually reflects recovery itself: blood loss and anemia, eating less, moving less, poor sleep and some medicines all reduce the heat your body makes. In an Australian and New Zealand study of major abdominal surgery, 59% of patients checked before discharge were anemic. Cold with fever, wound changes or breathlessness needs a clinician.
What to bring to the hospital to stay warm: a patient packing list
To stay warm in the hospital, pack layers you control: a robe, a front-opening sweater or zip top that clears IV lines and monitors, warm socks, slippers with non-slip soles and a firm fit, and a soft hat. Leave heating pads and electric blankets at home; many hospitals do not allow them, and nurses can bring warmed blankets instead.