Heat, cold and your body

A Korean bath is hot water, hot air and, if you want it, cold water, taken in turns over one to three hours. For most healthy adults this is safe; the sauna research finds regular heat bathing well tolerated. It is also real work for the heart. And of the bathhouse injuries recorded in Korea, most are slips and falls, not heat illness.

Every point below is marked official (fire authorities, the Korea Consumer Agency or the law), clinician (a named Korean doctor quoted in the press, no study cited), evidence (peer-reviewed research or a water-safety body) or claim. Where we have no source, we say so. The rooms guide gives the temperatures of each pool and room.

The rules in one place

Warning signs, and what to do

The fire authorities gave the advice in the table after two men died in separate bathhouses in Gyeonggi on the same day in May 2026. One was in his 60s and one in his 70s. Police suspected heart disease or a blood-pressure problem.

Heat raises pulse and blood pressure within minutes. It then widens the blood vessels, so pressure can drop, and blood moves to the skin and away from the brain (clinicians, 2001 and 2017). Act on these signs, in yourself or the person next to you: dizziness, a pale face, nausea or weakness. What to do (fire authorities; 2004 feature): leave the heat and sit or lie down somewhere cool. Sip water slowly. Do not pour cold water over someone who has fainted. Tell the staff.

The most serious warning comes from a 2001 clinician: a brief loss of consciousness in a tub can lead to drowning, and older adults with dulled sensation are at higher risk. Do not doze in a pool. If you feel unwell, get out.

Cold water

In the figures we have, the cold pool, naengtang (냉탕), is about 15°C. The RNLI, the UK and Ireland lifeboat charity, treats water at or below 15°C as cold. Evidence: sudden immersion in cold water triggers cold shock. You gasp without meaning to, your breathing can become up to ten times faster, and your heart rate and blood pressure jump. This can cause a heart attack even in young, healthy people. The first effects pass in under a minute; the RNLI advises waiting about a minute and controlling your breathing before you move.

Korean doctors disagree about hot–cold alternation. A rehabilitation-medicine professor (2001) said lay bathers should not do it at all. A 2015 health column said people with high blood pressure or angina should splash cold water on themselves instead of entering the cold pool. A 2026 article on contrast therapy quotes specialists who recommend about 15 minutes of heat, then 30 seconds to one minute of cold, two or three times a week. The same article says to avoid it entirely with heart disease, severe asthma, intense migraines or pregnancy, because heart patients risk arrhythmia. It also calls the recovery and "detox" benefits advocates' claims with limited evidence. A 2017 column explains that sudden cold after warmth constricts blood vessels, which can block or rupture them.

Our advice: enter slowly, never head first and never at a run. Go in to the knees, then the waist, and control your breathing. Skip the cold pool if you have any heart or blood-pressure condition, are pregnant, or feel unwell.

Who should be careful, and who should skip

Korean law requires a notice inside and outside every sweat room. It lists who should take care: children with colds, children under 5, and people weak from illness; people with systolic blood pressure of 180 or more; people at risk of cataracts or with facial flushing; the elderly; pregnant women; people with a high fever or severe heart disease; anyone who drank alcohol in the last two hours; and people who have lost a lot of blood. The law also bars entry to anyone with an infectious disease or too drunk to use the facility normally.

Clinicians go further. A health-screening doctor (2001) said people with high blood pressure, diabetes, severe obesity, shortness of breath or chest pain should generally avoid saunas and hot baths. A 2017 column adds older adults and post-menopausal women to the list for extra caution.

The research points the other way for one group. A 2018 review in Mayo Clinic Proceedings found regular Finnish sauna at 80–100°C well tolerated in stable cardiovascular disease, with no complex arrhythmias in heart patients. This applies to stable patients with their doctor's approval. It does not cover a 45°C pool. Where Korean caution and the Finnish data differ, we follow the caution.

• Pregnancy. It is on the posted list and in the 2026 contrast-therapy warning. We found no Korean guidance on a safe water temperature in pregnancy. Ask your doctor before you go.
• Children. The posted list covers children under 5 and children with colds or weak from illness. We found no Korean heat limit for children; we suggest keeping small children to the warm pool and the lounge. Which side of the bath a child may enter is a legal rule, covered in kids, families and special situations.
• Older visitors. Of recorded bathhouse injuries, 62.9% were to people aged 60 or over (see below). Clinicians recommend lukewarm water for older people and warn that dulled sensation makes overheating easy to miss.
• Medication. We found no Korean guidance on specific medicines; the posted notice lists conditions, not drugs. If you take anything for blood pressure or heart rhythm, ask your doctor before a long session.

Slips: the injury that actually happens

The Korea Consumer Agency's December 2025 report counted 1,790 bathhouse injuries from 2021 to June 2025. The yearly number rose from 151 in 2021 to 574 in 2024, an average increase of 56.1% a year. Of all the injuries, 89.3% were slips and falls, and 62.9% of the injured were aged 60 or over. Falls happen inside sweat rooms, around the edges of tubs, and in the changing room at the scales, sinks and water dispensers. In a survey of 16 Seoul bathhouses, none had anti-slip mats at those spots, and most changing rooms and sweat rooms had no slippery-floor warning. The cause the agency names: people walk around without drying off.

So dry off before you leave the bath hall, walk slowly, use a rail where there is one, and assume every floor is wet.

Hygiene: what the law covers and what it does not

Official. Bathhouses must clean changing rooms, lockers, tubs, sweat rooms, mats and lounges daily, disinfect the bathing room monthly, launder every towel and gown before it reaches a customer, and test the bath water at least once a year. Bathhouses that recirculate water must record water temperature and residual chlorine weekly and test for Legionella once a year. The allowed chlorine range was widened to 0.2–1 mg/L in June 2022. We found no rule on how often a tub must be fully drained, so we quote none. The Consumer Agency survey above shows that rules are not always followed.

Clinician. The infections dermatologists link to baths are ordinary ones. Athlete's foot (무좀) spreads through skin flakes on shared mats, towels and slippers. Dry between your toes, bring your own small towel and slippers, and do not treat it with vinegar or acids. Viral conjunctivitis spreads easily in hot, crowded baths: wash your hands and do not rub your eyes. Over-scrubbing can irritate the skin; see the seshin guide.

What is marketing

• Far-infrared (원적외선). Claimed to penetrate 4–5 cm, relieve neuralgia and arthritis, boost immunity and prevent cancer. The 2004 magazine that reported these claims said they lack medical evidence. A rehabilitation specialist (2001) said far-infrared penetrates only about 1–2 cm, that any benefit comes from ordinary radiant heat, and that no facility publishes measurements. Claim.
• Negative ions (음이온) and germanium. A Sogang University chemist (2018) said "negative ion" names no specific substance or function, that charged ions cannot stay stable in air, and that sitting on germanium ore is unlikely to affect the body. Claim.
• Detox, faster metabolism, better sleep, "skin glow" from hot–cold cycles. Advocates' claims with limited evidence (2026). Claim.
• Sweating off weight. The weight lost is water, and it returns when you drink (2001). Myth.
• Heat is good for you. Partly evidence: regular Finnish sauna is associated with lower rates of high blood pressure and cardiovascular disease. That is an association, not proof, and it concerns heat, not the stone in the wall.

When to skip the bath today

• A fever or an infectious disease. Fever is on the posted list. The law bars people with an infectious disease, and Sparex names infectious skin disease as a reason to refuse entry.
• A heart or blood-pressure problem that is not under control.
• Hunger, a heavy meal or exhaustion (clinician, 2001), or coming straight from the gym (2004 feature).
• A cold, unless you stay in the low-temperature room (2004 feature).
• Heavy drinking. The 2004 feature says to wait at least two hours, then take only a shower or a one- to two-minute soak.
• Simply feeling unwell.