Heat loosens and cold numbs, and either one can injure skin if left on too long

Key takeaways

• A 2006 Cochrane review found that heat wraps eased new low back pain a little after five days, while the few studies of cold were too poor to judge.
• Eye doctors advise a warm washcloth on a stye or chalazion for 10 to 15 minutes, three to five times a day, and in one study about half of chalazia cleared within three weeks with compresses alone.
• An Australian burn unit treated 11 people burned by microwaved wheat bags in five years, and 10 needed surgery; seven had diabetes or another condition that can dull feeling or slow reactions.
• Daily heat from a heating pad, hot water bottle or laptop can leave a lasting net-shaped brown mark called erythema ab igne, once nicknamed hot water bottle rash.
• The FDA says the most serious injuries from hot and cold therapy devices have come from cold, so keep a cloth between ice and skin and check underneath often.

A 42-year-old man went to his doctor for fatigue and chronic back pain that was getting worse¹. For relief, he had used a heating pad every day, often for hours at a time¹.

His doctors found a large brown patch with a lacy, net-like pattern across his back. It matched the spot where the heating pad sat¹. The diagnosis, published in 2018 in the Cleveland Clinic Journal of Medicine, was erythema ab igne, a skin change caused by repeated warmth¹.

Heat and cold are some of the most familiar comfort tools in any household. A hot water bottle, a bag of frozen peas or a warm washcloth costs almost nothing.

They also work in opposite ways, and each has a narrow set of jobs it does well. Used too hot, too cold or too long, either one can injure skin, and people who can’t feel their skin well are most at risk.

This guide covers what each one does, where the evidence holds up, how to stay safe, and a chooser to keep near the medicine cabinet.

Heat relaxes, cold numbs

The two tools pull in opposite directions. Heat loosens tense muscles and draws more blood to the area, according to Mayo Clinic Press³. Cold can numb pain and may tame some inflammation³.

That’s why the usual advice splits by timing. Mayo Clinic suggests cold for the first day or two after an injury and heat for tight, tense muscles³.

For a fresh sprain, Mayo Clinic advises ice for 15 to 20 minutes at a time, four to eight times a day, for the first 48 hours⁴. It warns that ice placed straight on skin, or left on too long, can damage tissue⁴.

Not every expert agrees that ice belongs in sprain care. A newer framework for soft-tissue injuries leaves it out, and our article on preventing exercise injuries covers that debate. If ice makes a sprain hurt less, treat it as comfort, not proof of faster healing.

For heat, Mayo Clinic Press suggests up to 20 minutes at a time, up to three times a day. Its rule for heating pads is blunt: never sleep with one³.

A heat wrap eases new back pain, a little

Low back pain is where heat has its best research. In 2006, a Cochrane team led by Simon French pooled nine trials with 1,117 people⁵. Cochrane is an international network that reviews health research.

Two trials with 258 people tested heat wraps. People with new or recent back pain who wore them had less pain after five days than people given a dummy pill⁵. The gain was small, about one point on a pain scale running from 0 to 5⁵.

One trial of 90 people found that a heated blanket eased new back pain right away⁵. Another, with 100 people, found that adding exercise to a heat wrap cut pain further after a week and improved function⁵.

Cold came up short. The reviewers found only three poor studies of cold therapy and drew no conclusions about it⁵. Studies comparing heat with cold disagreed⁵.

The reviewers called the evidence for heat wraps moderate but based on few trials. On our scale, that’s promising but early: a small, short-term boost, best paired with movement. Our article on rehabilitation covers what doctors’ guidelines say about back pain care.

A warm washcloth is the first step for eyelid bumps

Your eyelids hold tiny oil glands. When one gets blocked or infected, a bump called a chalazion or a stye can form⁶.

The American Academy of Ophthalmology (AAO) puts warmth first⁶. Its January 2026 guidance calls for a clean washcloth soaked in hot water and held on the eyelid for 10 to 15 minutes, three to five times a day⁶. Re-soak the cloth as it cools, and aim for warm, never hot enough to burn⁶.

The same page adds a few extras⁶:

• Hands off: squeezing or popping the bump can spread infection into the lid.
• Leave off eye makeup and contact lenses until it heals.
• With a chalazion, light massage around the bump with a clean finger can help the gland clear.

How well does it work? In a 2007 randomized study described by the AAO’s EyeNet magazine, 46% of chalazia cleared within three weeks with hot compresses⁷. A steroid shot plus massage cleared 84%, and a minor surgery cleared 87%⁷. Those results were gathered by phone from patients, which weakens them⁷.

So compresses are a sensible, low-cost first step, but not the fastest fix. See an ophthalmologist if a bump affects your vision, won’t go away or keeps coming back⁶. A bump that keeps returning may need a small tissue sample to rule out something more serious⁶.

Blepharitis, an eyelid condition, is a longer project. The AAO says it has no cure, but daily care can keep symptoms in check: a warm compress over closed eyes for at least a minute, plus gentle lid scrubs with baby shampoo diluted in warm water⁸. An eye doctor can add prescription treatments or in-office heat and massage for clogged glands⁸.

Cold has smaller wins: engorged breasts and migraines

Engorgement. In breast engorgement, the breasts become overly full, hard and sore during breastfeeding. Cold cabbage leaves are a kitchen remedy for it, and researchers have tested them.

A 2020 Cochrane review of 21 studies with 2,170 women looked at engorgement treatments⁹. Cold cabbage leaves may ease pain and hardness compared with routine care, and women were more satisfied with them⁹. Cold gel packs may also reduce hardness⁹. In one small trial, room-temperature cabbage leaves beat a hot water bottle⁹.

Every one of those findings was rated low or very low certainty⁹. The reviewers called several options promising but said they couldn’t draw firm conclusions⁹. Only three of the 21 studies reported on side effects at all⁹.

Migraine. A 2022 review led by Y.-Y. Hsu in the Journal of Clinical Nursing, as summarized by the medical news service MDedge, pooled six studies of cold for migraine, including cold-gel headbands, caps and mouth cooling¹⁰. Only four were randomized trials¹⁰. Pain scores dropped at 30 minutes, but the difference was no longer clear at 24 hours¹⁰. MDedge lists partial government funding and no declared conflicts¹⁰. Treat cold as a comfort measure that sits alongside your migraine plan, not as a replacement for it.

The evidence, rated

Below, we look at how the main uses of heat and cold stack up on our four-level scale.

Use	Rating	What the research shows
Heat wraps for new low back pain	Promising but early	Small, short-term relief in two trials; Cochrane called it moderate evidence5
Cold for low back pain	Not enough evidence	Only three poor-quality studies5
Warm compresses for chalazion	Promising but early	Standard first care; about half cleared in three weeks in one study67
Cold cabbage leaves or gel packs for engorgement	Promising but early	Possible relief, all low or very low certainty9
Cold for migraine pain	Promising but early	Short-term relief in six studies10
Ice speeds healing of a sprain	Not enough evidence	Widely advised for comfort4; see our injury article for the evidence debate
Heat or cold on numb skin	Evidence says no, or unsafe	Documented deep burns211; the FDA warns that dulled sensation raises cold-injury risk13

These results honor a tradition many readers value: caring for the body with simple, drug-free tools. A heat wrap or a warm washcloth involves no pills to swallow.

The tradition also carries wisdom about limits. Wrapping a hot water bottle in a towel is old household wisdom, and modern research mostly backs that instinct: comfort comes from moderate warmth or cold, for a short time, on skin that can feel it.

Heat burns happen most to skin that can’t feel it

Burns from home heat packs are uncommon, but they can be deep. The Royal Adelaide Hospital burns unit in Australia counted 11 patients burned by microwaved wheat bags over five years, out of 1,913 admissions².

Seven of the 11 had a condition that could dull feeling or slow reactions, such as diabetes, multiple sclerosis or spina bifida². Ten needed surgery, and one lost all the toes on one foot². Feet were the most common burn site².

The team then heated three wheat bags in the lab. Heated as directed, the hottest bag reached about 57°C (135°F)². In a stronger 1,000-watt microwave, readings climbed as high as 65°C, and reheating a bag before it had cooled drove temperatures near 70°C, with one reading of 75°C². The instructions covered only certain microwave strengths².

An older American study shows the same pattern. In 1987, doctors in Madison, Wisconsin, looked back at 15 years of burn care for people with diabetes at four hospitals and found 10 leg or foot burns tied to lost feeling¹¹. All 10 patients had nerve damage, called neuropathy¹¹. Five were scalded by hot tap water used for foot care, and two by a hot, moist compress or heating pad placed on leg sores or skin infections¹¹.

The authors urged doctors to warn patients with diabetes about heating pads and hot compresses and to test water before a foot soak¹¹.

Heat combined with muscle rubs adds another risk; our article on herbal preparation forms covers the FDA’s warning.

Daily heat can leave a lasting mark

Erythema ab igne, once nicknamed hot water bottle rash, comes from repeated exposure to warmth rather than a single burn¹¹². It starts as redness that doesn’t fade and, in long-standing cases, darkens into a lacy brown pattern¹.

Heating pads and hot water bottles are the most often reported causes¹. A 2017 case report adds laptops, heated car seats, space heaters and electric blankets to the list¹². Its authors describe repeated exposure to temperatures close to the burn threshold, about 43 to 47°C (109 to 117°F)¹².

The mark is more than cosmetic. Long-standing patches carry a small extra risk of skin cancer, especially squamous cell carcinoma in skin that thins or won’t heal¹. The first treatment is to stop the heat, and the color may fade slowly over several years¹.

There’s a second message in that rash. If you need heat every day to get through the day, the pain itself deserves a checkup. The 2017 report notes that chronic pain and lasting body-wide symptoms should be looked into for an underlying illness¹².

Cold can injure, too

Cold packs feel harmless, but the FDA has linked the most serious skin and tissue injuries from hot and cold therapy devices to cold¹³. Injuries range from numbness to frostbite, and serious cases can require skin grafts or amputation¹³.

Water-circulating cold machines stay cold longer than an ice pack¹³. The FDA’s advice for these devices makes sense, in our view, for any cold pack¹³:

• Keep a cloth between the pack and your skin, and don’t strap it on too tightly.
• Check the skin underneath often and keep it dry.
• Stop and call your provider for numbness, new or worse pain, burning, itching, blisters, swelling, redness or color changes.

Conditions that slow blood flow or dull skin sensation make injury more likely, the FDA notes¹³. Tell your clinician about them before using a cold device.

Raynaud’s phenomenon is a cold-sensitive condition. In an attack, fingers or toes turn white or blue and go cold and numb¹⁴. The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) names getting cold, such as holding a glass of ice water, as the most common trigger and advises gloves for frozen items¹⁴. If you have Raynaud’s, ask your clinician before using ice packs¹³¹⁴.

Heat or cold? A chooser

This chooser is ours, built from the sources above. Time limits come from clinical advice, not trials. Check the skin often during any session, as the FDA advises¹³.

Problem	Which	How long	Skin check	See a clinician if…
Fresh sprain or strain	Cold, if it helps the pain4	15 to 20 minutes, 4 to 8 times a day, first 48 hours4	Cloth barrier; stop if numb, discolored or blistered413	You can’t bear weight, the joint feels unstable, it hurts over the bone, or there’s no improvement in 2 to 3 days4
New low back pain	Heat wrap or pad5	Up to 20 minutes, up to 3 times a day for pads3	Never sleep on a pad3	You need heat daily for weeks12
Stiff, achy muscles	Heat3	Up to 20 minutes3	Warm, not hot; check for redness that lingers1	A net-like rash appears where heat sits1
Stye or chalazion	Warm washcloth6	10 to 15 minutes, 3 to 5 times a day6	Warm enough to help, not to burn6	Vision is affected, or it lasts or keeps coming back6
Blepharitis	Warm compress plus lid scrubs8	At least 1 minute8	Closed eyes; clean cloth8	Symptoms continue despite daily care (our suggestion)
Engorged breasts	Cold cabbage leaves or gel pack9	Not set by the review	Check skin under the pack (our suggestion)	Pain keeps worsening (our suggestion)
Migraine pain	Cold pack on the head10	Relief was measured at 30 minutes10	Cloth barrier13	Headaches change pattern (our suggestion)
Raynaud’s attack	Gentle warmth, not ice14	Until the attack passes (our suggestion)	Warm, not hot water14	Attacks are frequent or severe (our suggestion)
Minor burn from a pack	Cool running water, not ice15	10 to 20 minutes15	Leave blisters intact15	Deep or large burns, or burns on the face, hands, feet, groin or a major joint15

Reporting a problem. If a heating pad, cold pack or therapy machine injures you, the FDA asks you to report it through MedWatch, its safety reporting program¹³.

Questions readers ask

The bottom line

Heat and cold are honest, low-cost tools with modest, specific jobs. A heat wrap can take the edge off new back pain, a warm washcloth is the first step for a stye or chalazion, and cold may ease a sprain, engorged breasts or a migraine for a while.

The risks come from too much heat or cold, for too long, on skin that can’t warn you. Keep a cloth barrier, stop at about 20 minutes, never sleep on a heating pad, and get daily pain or a lingering eyelid bump checked.

Keep exploring: salt water gargle for colds.

Related reading

• What prevents running injuries after the 10% rule failed its biggest test
• Most back pain fades on its own, and dizziness and bladder leaks respond to rehab
• Water, alcohol or oil: how an herb’s form changes what you get
• A cold plunge eases soreness but can shrink your muscle gains
• Plain water gargles cut colds in one trial, while steam bowls have burned children

Sources

1. Smith TS III, Nambudiri VE. “Erythema ab igne.” Cleveland Clinic Journal of Medicine, 2018;85(2):96-97. pubmed.ncbi.nlm.nih.gov
2. Collins A, Amprayil M, Solanki NS, Greenwood JE. “Burns From Hot Wheat Bags: A Public Safety Issue.” ePlasty, 2011;11:e36. hmpgloballearningnetwork.com
3. Mayo Clinic Press (excerpt from Back and Neck Health). “Using heat and cold for pain.” Mayo Clinic Connect, 2021. connect.mayoclinic.org
4. Mayo Clinic Staff. “Sprain: First aid.” Mayo Clinic, 2024. mayoclinic.org
5. French SD, Cameron M, Walker BF, Reggars JW, Esterman AJ. “Superficial heat or cold for low back pain.” Cochrane Database of Systematic Reviews, 2006, Issue 1, CD004750. vuir.vu.edu.au
6. American Academy of Ophthalmology. “What Is the Difference Between a Stye and a Chalazion?” AAO, 2026. aao.org
7. American Academy of Ophthalmology, EyeNet. “Chalazion Management: Evidence and Questions.” AAO. aao.org
8. American Academy of Ophthalmology. “What Is Blepharitis?” AAO, 2025. aao.org
9. Zakarija-Grkovic I, Stewart F. “Treatments for breast engorgement during lactation.” Cochrane Database of Systematic Reviews, 2020, Issue 9, CD006946. cochranelibrary.com
10. MDedge Clinical Edge Journal Scan. “Cold treatment provides instant relief from migraine pain” (summary of Hsu Y-Y et al., “Cold intervention for relieving migraine symptoms,” Journal of Clinical Nursing, 2022). MDedge, 2022. mdedge.com
11. Katcher ML, Shapiro MM. “Lower Extremity Burns Related to Sensory Loss in Diabetes Mellitus.” Journal of Family Practice, 1987;24(2):149-151. pubmed.ncbi.nlm.nih.gov
12. Guarneri C, Tchernev G, Wollina U, Lotti T, Vaccaro M. “Erythema Ab Igne Caused By Laptop Computer.” Open Access Macedonian Journal of Medical Sciences, 2017. oamjms.eu
13. U.S. Food and Drug Administration. “Cold Facts to Help Avoid Injury from Water-Circulating Hot/Cold Therapy Devices.” FDA Consumer Update, 2020. fda.gov
14. National Institute of Arthritis and Musculoskeletal and Skin Diseases. “Raynaud’s Phenomenon.” NIAMS, NIH. niams.nih.gov
15. Mayo Clinic Staff. “Burns: Diagnosis and treatment.” Mayo Clinic, 2024. mayoclinic.org