Hot spring safety: who shouldn't soak, and for how long

Most healthy adults can soak in a Malaysian hot spring safely if they keep each dip to about 10 to 15 minutes in water around 40°C, drink water, and stay off alcohol. The people who need to be more careful, or check with a doctor first, are those with heart disease, pregnant women (especially early on), young children, people with diabetes who have numb feet, and anyone on medicines that affect blood pressure or sweating. And no one should touch the water at the source vents, which at some Malaysian springs comes out at 70°C to 100°C.

Most of what follows comes from studies of hot tubs, home baths and heat in general, not Malaysian springs. We say so where it matters. For what soaking may do for you, see the health benefits evidence.

Who should be careful

Who	Main risk	What to do
Heart disease, past stroke, very high or low blood pressure	Blood pressure drop, fainting, drowning	Ask your doctor first. Short dips, never alone
Treated high blood pressure, stable	Light-headedness when standing up	10 minutes at about 40°C, get out slowly [1]
Pregnant, especially first 3 months	Raised core temperature linked to birth defects	Lukewarm pools, under 20 minutes, ask your doctor [4] [6]
Children	Drowning, scalds	Hands-on supervision, cooler pools, short dips [7] [8]
Diabetes with numb feet	Burns you don’t feel, slow-healing wounds	Test water with your hand or elbow, check feet after [9]
On diuretics, beta blockers, antipsychotics or similar	Worse heat tolerance	Shorter soaks, more water, ask your pharmacist [3] [10]
Open wounds, fresh tattoos, skin infection	Infection	Stay out until healed
After drinking alcohol	Fainting, drowning	Don’t soak [2] [7]

Is it safe to soak with high blood pressure or heart disease?

For stable, treated high blood pressure, the best direct evidence is reassuring but small. In a Canadian trial, 21 people on blood pressure medicine sat in a 40°C hot tub for 10 minutes. Their systolic pressure fell from an average 144 to 122 mmHg, about the same drop as in 23 people without hypertension, and it returned toward normal within 10 minutes of getting out. Nobody reported dizziness, chest pain or palpitations [1].

The authors’ caveats matter at a hot spring. Blood pressure was measured sitting down, and they expected bigger drops when people stand up. No one was on nitrate heart medicines, and the trial lasted 10 minutes, not an afternoon [1].

Heart disease is a different matter. People with weak heart function struggle to raise their heart output enough to cool themselves through the skin [3]. In 3,289 bath-related deaths investigated in Tokyo, most were in people over 60, and among the 550 autopsied, 54.5% had circulatory disease and 79.1% showed signs of drowning. The authors concluded that heart and circulation problems were the likely underlying cause and drowning often the final step [2]. If you have heart disease or have had a stroke, get your doctor’s view before you go, and never soak alone.

Can you go in a hot spring while pregnant?

The concern is overheating your core, not the water itself. A meta-analysis of 15 studies found that high body temperature in early pregnancy, from fever, hot tubs or saunas, was linked with roughly double the odds of neural tube defects such as spina bifida (odds ratio 1.92) [4]. A large US case-control study found hot tub use in early pregnancy linked with gastroschisis and anencephaly, with higher odds in women who used one repeatedly for over 30 minutes. The authors warned that some of these links could be due to chance [5].

The reassuring side: a review of 12 studies (347 pregnant women) found no one reached the 39°C core temperature linked to birth defects. The authors concluded that sitting in a 40°C bath for up to 20 minutes kept women below that line [6].

So if you’re pregnant and your doctor is fine with it, pick a pool you can sit in comfortably, not the hottest one, keep it under 20 minutes, and get out if you feel hot, faint or nauseous. In the first trimester, our cautious suggestion is to soak your feet only. That isn’t a study finding: the reason is that most Malaysian pools don’t post their temperature, so you can’t be sure you’re at 40°C or below.

Are hot springs safe for children?

The biggest danger to children is drowning, not heat. In a 1991 US review of 151 spa and hot tub deaths, 61 were children under 12, and drowning in uncovered or poorly covered tubs was the leading cause [7].

Children also scald more easily. A UK care guideline, cited by Malaysian researchers studying Hulu Langat springs, puts the safe limit for bathing water at 44°C, and lists children and older people among those most at risk of scalds [8].

We found no evidence-based soak time for children. The researchers in the blood pressure trial flagged children as a group their results might not apply to [1]. Our suggestion: a few minutes at a time in the coolest pool, an adult within arm’s reach, and out at once if they look flushed or say they feel unwell.

Why alcohol and hot springs don’t mix

Alcohol was the most common risk factor in the US hot tub deaths, ahead of heart disease [7]. In the Tokyo bath deaths, 140 of the 550 autopsied cases, about a quarter, had blood alcohol above 0.5 mg/mL, and the authors’ advice was blunt: people who have been drinking should not bathe [2]. Save the drink for after you’ve dried off and cooled down.

Diabetes and numb feet: the burn you don’t feel

Nerve damage from diabetes can stop you feeling heat on your feet until the skin is already burnt. In a US burn unit study, adults with diabetes were far more likely to have burnt feet than other adult patients, of whom 14% had foot burns. Scalds and contact with hot surfaces were the main causes, people with diabetes came in later for treatment, and they had more wound infections. The authors suspected nerve damage played a part [9].

Diabetes can also reduce sweating and blood flow to the skin, which makes it harder to shed heat [3]. If you have diabetes, test every pool with your hand or elbow before stepping in, avoid walking barefoot on hot rock near the vents, and check your feet for redness or blisters afterwards.

Medicines that make heat harder to handle

Some common medicines reduce how well the body copes with heat. A study of older US patients with chronic illness looked at diuretics, anticholinergics, antipsychotics, beta blockers, stimulants and other blood pressure drugs. Over US summers, several of these classes were linked with 16% to 37% higher rates of heat-related hospital admission while people were taking them, even outside heatwaves [10]. A review of heat stress in older people makes the same point about diuretics, vasodilators and beta blockers [3]. These were not hot spring users, but the mechanism is the same: less sweating, less fluid, or a blunted heart rate response.

Don’t stop any medicine to go soaking. Ask your doctor or pharmacist if yours affects heat tolerance, and if it does, keep dips short and drink more.

Heat exhaustion and dehydration in Malaysia’s climate

At an open-air spring on a hot afternoon, you take in heat from the water and the air at once. Above 35°C in high humidity, sweating barely cools you [17]. Losing as little as 1% of body weight in fluid can impair the heart and temperature control, and older adults take longer to recover from dehydration [3].

Get out, sit in the shade and drink water if you feel dizzy, weak, headachy or sick. Those are early signs of overheating. Confusion, clumsiness or collapse can mean heatstroke, which is an emergency: call 999 and cool the person down [17].

Timing helps too. An early morning or evening soak keeps the midday sun off you on top of the water’s heat.

How long and how hot should you soak?

Water temperature	What it means	Who it suits
Up to about 38°C	Warm. Feels close to body temperature	Children, pregnant women, first-timers
About 40°C	The temperature used in the hypertension and pregnancy studies [1] [6]	Most adults, 10–15 minutes per dip; up to 20 minutes if pregnant and cleared by a doctor
41–44°C	Hot. 44°C is the upper limit for bathing water in a UK home care guideline [8]	Healthy adults, short dips
Above 44°C	Scald risk rises, especially for children and older people [8]	Feet only, briefly, or not at all
60°C and above	Source vents and egg pools	Nobody

Most public pools don’t post temperatures. Test with your hand, start in the coolest pool, and go up only if you’re comfortable. Between dips, sit out, cool down and drink water. Several short soaks are safer than one long one.

Egg-boiling pools: how hot Malaysian source water gets

Almost all Malaysian springs are non-volcanic (the one volcanic-related system is in Sabah), but the water at the source can still be close to boiling. Geologists recorded up to 100.2°C at Sungai Klah (Felda Residence) in Perak [11]. At the Pos Hendrop spring in Lojing, Kelantan, the main vent measured 72.31°C, 30 minutes there produced only half-cooked eggs, and the researchers advised against any direct body contact [12]. In Hulu Langat, Selangor, the hottest points sampled, at a spring inside a youth skills institute (IKBN), measured 70.41°C to 74.03°C [8].

Use the baskets or bags provided, keep children well back from the vents, and don’t reach into the water for a dropped egg. At wild springs such as Ulu Slim there are no barriers between the path and the near-boiling pools. At Kuala Woh the hot water rises on a riverbank, so how hot your spot is depends on how close you sit to the source.

Hygiene, amoebas and open wounds

Warm freshwater is where Naegleria fowleri, the “brain-eating amoeba”, lives. It enters through the nose and causes a brain infection that killed 92% of 380 people with known outcomes in a global review. About 8% of cases with a known water source involved geothermal water [13]. Infections are extremely rare.

No case has been reported in Malaysia. A 2011 study of pools, lakes and streams in Selangor and Kuala Lumpur found only harmless Naegleria species, and noted that N. fowleri had never been isolated in Malaysia. It did not sample hot springs [14]. In 2022 the Ministry of Health said there had been no cases in the country. It listed hot springs among the places the amoeba can live, and advised against stirring up sediment and against diving or jumping in, which forces water up the nose [15].

So keep your head above water, don’t dive or jump in, and don’t splash water into your nose. If fever, headache, vomiting or a stiff neck come on after a swim or soak, see a doctor quickly and say where you’ve been [15].

Treated hot tubs need chlorine, and hotter water burns it off faster. When chlorine levels dropped in US hotel hot tubs, guests got itchy Pseudomonas skin rashes [16]. Natural spring pools are usually not chlorinated at all, which is why open wounds, fresh tattoos and active skin infections should stay out until healed. Rinse with clean water afterwards, and don’t drink spring water.

A quick safety checklist

• Check with your doctor first if you have heart disease, are pregnant, or have diabetes with numb feet.
• Eat lightly beforehand, and bring at least a litre of water per person.
• No alcohol before or during.
• Test every pool with your hand. Start in the coolest one.
• 10–15 minutes per dip, then sit out and cool down.
• Never soak alone if you are older or have a heart condition.
• Children: arm’s reach, short dips, cooler pools.
• Stay well away from vents and egg pools.
• Keep water out of your nose, and keep open wounds out of the water.
• Get out slowly, holding a rail if there is one.

Soaking safely at Malaysian springs

For children, pregnant women and anyone with a heart condition, the easiest places are managed sites with a cooler pool and people around. Suria Hot Spring Bentong has separate hot, cool and children’s pools. Serai Bamboo has a shallow kids’ pool, and at Poring in Sabah the spring water is piped into tubs, so you can let it cool before getting in.

Some public pools are simply too hot to sit in. At Dusun Tua in Hulu Langat, the water reaches the basin at about 60°C, so you scoop it over yourself instead of getting in, which is a sensible way to control the heat. Riverbank springs such as Kuala Woh add slippery rocks and open river water, so go as a group.

Each spring page lists reported water temperatures where we could find a source. Where no figure exists, assume the water near the source is too hot to touch until you’ve tested it.