Hot spring health benefits: what the research shows

In trials, courses of spa bathing eased knee osteoarthritis pain for months afterwards, and a few small trials found something similar for chronic low back pain and fibromyalgia. A warm soak an hour or two before bed helped people fall asleep faster, though those studies used home baths. Claims about skin disease, stress and heart health rest on small, uncontrolled or observational studies, many of them not done in hot springs at all. The Malaysian springs that have been tested are low in minerals, so any benefit from a soak here most likely comes from the heat and the water, not from special minerals.

Below, each claim gets one of four grades: strong (consistent, good-quality trials), moderate (several trials point the same way, with real weaknesses), limited (small, uncontrolled, lab or observational studies) or traditional (folk practice without trial data). Nothing here has reached “strong”.

Hot spring benefits at a glance

Claim	What studies found	Grade
Less knee arthritis pain	Less pain and better function 2–12 months after a course of spa bathing, in reviews of 7–8 trials and one 382-person trial [1] [2] [3]	Moderate
Less chronic low back pain	About 19–27 mm less pain on a 100 mm scale across 5 trials [4]	Limited
Fibromyalgia pain	Less pain in 5 small mineral-bath trials, none at low risk of bias [5]	Limited
Psoriasis and eczema	Narrative reviews of famous spa sites like the Dead Sea, and one uncontrolled Japanese series [6] [7] [8]	Limited
Falling asleep faster	A 40–42.5°C bath 1–2 hours before bed shortened time to sleep [9]	Moderate (warm baths, not hot springs)
Lower stress hormones	Cortisol changed in some studies, not others [10]	Limited
Heart and blood vessels	Better artery function in a 20-person lab trial; lower heart disease and stroke rates in people who bathe often [11] [12] [13]	Limited

Do hot springs help arthritis and joint pain?

Knee osteoarthritis is the best-studied use of mineral or thermal water bathing. A Cochrane review included 7 randomised trials with 498 people with osteoarthritis. Mineral baths beat no treatment for pain and quality of life, but the authors called the evidence weak because the trials were poorly designed and reported [1]. Its searches ended in 2006, so newer trials are not in it.

A later meta-analysis of 8 knee trials (359 treated, 375 controls) found less pain and stiffness and better function 2 to 12 months after treatment. The results varied a lot between trials, which the authors put down to study quality [2].

The largest single trial, from France, analysed 382 people with knee osteoarthritis. Everyone kept their usual medicine and did home exercises; about half also got 18 days of spa therapy. Six months later, 50.8% of the spa group had a meaningful improvement in pain or function, against 36.4% of the others. Quality of life scores did not improve [3].

One catch: that French package included massage, showers and mud as well as pool sessions. A soak at a roadside kolam is not the same treatment, and we found no similar trial in Malaysia.

Can hot springs ease chronic low back pain?

A meta-analysis of 5 randomised trials found that people with chronic low back pain who had spa therapy reported about 27 mm less pain on a 100 mm scale than people on a waiting list (442 people). Bathing alone, without the other spa treatments, gave about 19 mm less pain than control groups (138 people) [4].

The authors called the data scarce and “not compelling”, and asked for large, rigorous trials. The review is also from 2006, so treat it as an early signal, not a settled answer.

What about fibromyalgia?

A 2014 meta-analysis split water treatments into two groups [5]. Exercise in ordinary warm pools gave a small drop in pain and a small gain in quality of life across 8 trials. Baths in mineral or thermal water, the closest match to a hot spring soak, showed a larger drop in pain across 5 trials with 177 people. But none of those 5 trials was at low risk of bias, most had fewer than 25 people per group, and the authors warned that the benefit of mineral baths may be overestimated.

Is it the minerals or just the heat?

Trials rarely separate the two. In the Cochrane review, the combination of sulphur and Dead Sea baths helped at the end of treatment, but sulphur baths alone or Dead Sea baths alone did not beat no treatment [1]. In the back pain review, trials of full spa packages showed a larger pooled effect than trials of bathing alone [4].

Few trials compare mineral water with plain warm water under the same conditions, so it is hard to say how much the minerals add. Warmth, buoyancy, rest and a break from routine all plausibly play a part. We look at magnesium and sulphur and sulphate in separate posts, and at how traditional Chinese medicine explains warm-water bathing.

Hot springs for psoriasis, eczema and other skin conditions

Dermatology reviews describe a long history of bathing for psoriasis and atopic dermatitis (eczema), with the Dead Sea, La Roche-Posay and the Blue Lagoon among the best-known sites [6] [7]. These are narrative reviews, not pooled trials. One notes that the climate at these centres helps skin on its own, and that UV light treatment is often added to the bathing [7].

A widely cited hot spring study for eczema comes from doctors at Kusatsu, a Japanese spa town with acidic water. Seventy people with hard-to-treat atopic dermatitis took a 10-minute, 42°C bath in the acidic spring water twice a day. Skin improved in 76% of them, and in 30 of 42 responders who were checked, Staphylococcus aureus bacteria on the skin fell or disappeared. There was no comparison group [8].

That matters here. The Selangor and KL springs that have been tested are neutral to slightly alkaline, with a pH of about 6.8 to 9.0, not acidic [14] [15]. Their sulphate, at 0.15 to 1.51 mg/L, is hundreds of times lower than the 611 mg/L quoted for Kusatsu water [14]. A result from strongly mineralised, acidic water does not carry over to water this different.

If you have eczema or psoriasis, hot water can also dry or irritate skin. Ask your dermatologist before trying it, and rinse and moisturise afterwards.

Do hot springs help you sleep better?

A 2019 meta-analysis of 17 studies looked at warm baths and showers before bed. Water at 40–42.5°C taken 1 to 2 hours before bedtime was linked with better self-rated sleep and sleep efficiency, and even 10 minutes was enough to shorten the time it took to fall asleep [9].

The likely reason is that warming the skin speeds up heat loss afterwards, and a falling core temperature helps trigger sleep. These were home baths and showers; no one has tested a hot spring soak for sleep. If you want to try it, go in the evening rather than at midday. Sungai Lalang in Semenyih opens again from 4.30pm to 10pm, and Hulu Tamu near Batang Kali is reported to stay open until 10pm. Check the current hours on each page first.

Can hot springs lower stress?

A systematic review of 15 studies (684 people) looked at cortisol, a stress hormone. Of 5 studies on bathing alone, 2 found cortisol changes in healthy people and 3 found no change in people with rheumatic disease. Spa programmes that combined bathing with other treatments changed cortisol in 8 of 10 studies [10].

The authors concluded that bathing may help manage stress, but called the data limited. Many people feel calmer after a soak; whether that lasts or measurably changes stress biology is not yet clear.

Is hot water bathing good for your heart?

Heat makes blood vessels widen and the heart pump more, much as light exercise does. In a US lab trial, 10 young, inactive adults soaked in 40.5°C water 4 to 5 times a week for 8 weeks, keeping their core temperature at 38.5°C or above for an hour each time. Their arteries became more flexible and their mean blood pressure fell from 83 to 78 mmHg, while a comparison group soaking in water near skin temperature showed no change [11].

Two Japanese studies point the same way, but they are observational. Among 873 middle-aged and older adults, those who took hot baths at least 5 times a week had less arterial stiffness and lower levels of a heart strain marker [12]. In a study that followed 30,076 people aged 40 to 59 for about 20 years, those who bathed almost daily had a 28% lower risk of cardiovascular disease than those who bathed 0 to 2 times a week. There was no difference for sudden cardiac death [13].

People who bathe daily may differ in other ways, so these studies cannot prove cause. They are also about home tub baths, not hot springs. And the US trial used far more heat than a casual visitor should try at a wild spring.

Who should be careful

Heat strains the circulation, which is where most of the risk sits. Medical examiners in Tokyo reviewed 3,289 bath-related deaths over three years. Most were people over 60. Among the 550 autopsied, more than half had circulatory disease, most showed signs of drowning, and about a quarter had been drinking [16].

Check with a doctor before soaking if you:

• have heart disease, have had a stroke, or have high or very low blood pressure
• are pregnant
• have diabetes with numb feet, or any condition that makes it hard to feel heat
• have open wounds or an active skin infection
• are older and plan to bathe alone

A UK care guideline cited by Malaysian researchers puts the safe limit for bathing water at 44°C, and names children, older people and people with limited mobility as most at risk of scalding [15]. Some Malaysian sources run far hotter: water at the spring source inside the IKBN training institute in Hulu Langat measured 74°C [15]. Skip alcohol before and during a soak, and do not drink the spring water: Selangor samples did not meet Malaysia’s drinking water standard [14]. Our safety guide covers infections, burns and fainting in more detail.

What’s actually in Malaysian hot spring water

A USM PhD thesis identified 60 hot springs across Peninsular Malaysia. All are non-volcanic: rainwater seeps deep along fault lines in granite country, heats up, and comes back up as mostly sodium bicarbonate water [17].

Researchers from UiTM sampled 11 sites in Selangor and KL, including Kerling, Kuala Kubu Bharu, Hulu Tamu, Hulu Yam, Selayang and Setapak. Water temperature ranged from 36.1°C to 67.9°C, pH from 7.1 to 9.0, and sulphate was low at 0.15 to 1.51 mg/L. The rotten-egg smell at some springs comes from hydrogen sulphide gas, a different form of sulphur [14].

A Sains Malaysiana study of Hulu Langat springs, including Dusun Tua, Sungai Serai and Sungai Lalang, found silica at 28 to 45 mg/L but magnesium at only 0.01 to 0.06 mg/L. Earlier studies the authors compared against found up to about 0.2 mg/L of magnesium, still a trace [15].

The Hulu Langat authors suggested the trace elements could help skin conditions like psoriasis and eczema [15], but that was based on water chemistry, not on testing anyone’s skin. We found no published trial testing a Malaysian spring on patients.

How to soak for the benefits the research supports

• Aim for 40–42°C, not the hottest pool. That is the range used in the sleep and eczema studies [8] [9]. Test with your hand, and use the cooler pools at hot sites.
• Keep it short. 10 to 15 minutes per dip is in line with the studies; Japanese adults in one study averaged about 12 minutes per bath [12]. Get out, cool down, drink water, then go back in if you want.
• For sleep, go late. Plan the soak 1 to 2 hours before bed [9].
• For joint pain, think in courses. The trials used repeated sessions over at least 2 to 3 weeks, not one visit [2] [3]. Keep doing your exercises and taking your usual treatment alongside.
• Go with someone. Most bath-related deaths in the Tokyo data were in people over 60, often with circulatory disease, and many showed signs of drowning [16]. Someone nearby can pull you out.