Magnesium in hot springs: can your skin absorb it?

Probably not in any amount that matters. Healthy skin is built to keep dissolved salts out, and the human studies claiming otherwise are small, short or were never peer reviewed [1]. On top of that, five of the six Malaysian springs in the one lab study we found held less magnesium per litre than your own blood does, so there is very little to absorb in the first place.

That doesn’t make a soak pointless. Magnesium-rich salt water may do something for the surface of the skin, and hot water has real effects on the body. Below is what the research actually shows, and what is in the water at Malaysian springs.

Can skin absorb magnesium at all?

The outer layer of skin, the stratum corneum, is 15 to 20 layers of flattened dead cells set in a fatty matrix. Fat-soluble substances get through it slowly. Charged particles mostly don’t. Magnesium dissolved in water is a charged ion wrapped in a shell of water molecules, which is why it is expected to cross intact skin poorly [1].

The weak points in the barrier are hair follicles and sweat glands. A 2016 lab study on human skin found that magnesium did get into the stratum corneum, more at higher concentrations and with longer contact, and that hair follicles carried a large share of it [2].

The catch: follicles and sweat glands make up only about 0.1% to 1% of the skin’s surface, and that study did not report how much magnesium got through [1]. “Some gets in” is a long way from “enough to change your magnesium levels”.

What human studies on transdermal magnesium found

In 2017, Gröber and colleagues reviewed the evidence under the title “Myth or Reality: Transdermal Magnesium?”. Their conclusion was blunt: they could not yet recommend transdermal magnesium, and they warned against using it in place of proven oral treatment for genuine deficiency [1].

Here are the studies most often quoted, with what they really tested:

Study	Who and what	What happened	The catch
Magnesium cream pilot, 2017 [3]	25 adults, magnesium cream (56 mg a day) or placebo cream for 2 weeks	Blood magnesium rose from 0.82 to 0.89 mmol/L, not statistically significant overall	Significant only in a subgroup of non-athletes. One author declared a future commercial interest in a magnesium cream
Epsom salt bath report (described in [1])	19 people, 12-minute Epsom salt baths for 7 days	Blood and urine magnesium rose	Posted only on the Epsom Salt Council’s commercial website, never peer reviewed
Magnesium oil spray study (described in [1])	9 people, 12 weeks of sprays and foot soaks	Magnesium in hair samples rose	Tiny group, measured hair not blood
Magnesium lotion safety trial (described in [1])	34 healthy volunteers, randomised to a magnesium sulphate lotion or placebo, 3 times a day for 3 days	No difference in blood magnesium	Short, but randomised and placebo-controlled
Bath spa water immersion, 1985 [4]	8 healthy people sitting in spa water at 35°C for 2 hours	No change in plasma magnesium [1]; urine output doubled	Very small, single session

The pattern is hard to miss. The better controlled the study, the smaller the effect. No one has run a large randomised trial of mineral bathing and magnesium status.

What the Dead Sea studies show

Putting magnesium on the skin is one of the oldest skin treatments, with Dead Sea therapy and Epsom salt baths as the classic examples [2]. The Dead Sea is one of the saltiest lakes on earth, and its treatments are well studied for psoriasis [5]. A 1985 study measured blood minerals in healthy volunteers and psoriasis patients after bathing in the Dead Sea or in simulated salt solutions [6].

Bromine, rubidium, calcium and zinc rose in the blood, but only in the psoriasis patients, whose skin barrier is damaged, and only after four weeks of daily bathing. Magnesium was not among them. The magnesium result came from guinea pigs bathed in salt solutions with radioactive tracers, where traces turned up in the blood after an hour. The authors concluded that salts do cross healthy skin, but every rise in human blood levels they measured was in psoriasis patients [6].

A 2012 systematic review found good evidence that Dead Sea treatment helps psoriasis [5]. But the reviewers credited the region’s unusual sunlight as well as the water, so the share that comes from the minerals alone is hard to pin down.

So even in water far saltier than any Malaysian spring, there is little direct evidence that healthy human skin takes in meaningful amounts of magnesium.

Magnesium and the skin barrier: a more plausible benefit

There is a second, better-supported idea: magnesium salts may help the skin from the outside, without needing to reach your bloodstream.

In a German study, people with dry, atopic skin soaked one forearm for 15 minutes in a 5% solution of a magnesium-rich Dead Sea salt and the other forearm in tap water, over six weeks [7]. The salt-soaked arm ended up better hydrated, less rough and less red. In the subgroup whose skin was losing more water at the start (a sign of a leaky barrier), barrier function improved compared with the tap water arm.

In hairless mice, three of the four magnesium salts tested sped up skin barrier repair after the barrier was deliberately damaged. An equal mix of magnesium chloride and calcium chloride worked better than magnesium chloride alone [8].

Keep these in proportion. The human study tested only forearms with a commercial salt product, and the other is an animal study. Also look at the dose: a 5% salt solution is 50 grams of salt per litre, a far stronger brine than the inland Malaysian springs in the table below.

How much magnesium is in Malaysian hot spring water?

Mineral data for individual Malaysian springs is rarely published. The most useful set of numbers we found comes from a study led by Universiti Teknologi Malaysia researchers, who sent water from six springs to a commercial lab for analysis using standard APHA and US EPA methods [9]. Here is how they compare with your blood and with seawater:

Water	Magnesium (mg per litre)	Notes
Dusun Tua, Hulu Langat	under 0.1	70°C at the sampling point
Sungai Serai, Hulu Langat	0.2	43°C
Semenyih, Selangor	0.2	43°C
Sungai Klah (Felda Residence), Perak	0.5	75°C
Ulu Slim, Perak	0.8	90°C
Human blood serum	about 19	0.8 mmol/L [1]
Ayer Hangat, Langkawi	394	45°C, salty water
Seawater	about 1,340	55 mmol/L [1]

Blood and seawater figures are converted from mmol/L (1 mmol of magnesium is about 24.3 mg). Spring figures are from Chan et al. [9].

The inland springs along the Titiwangsa range are low-mineral water. Of the metals measured, sodium was highest (27 to 51 mg/L) and magnesium barely registered. The case for absorbing magnesium from seawater rests on its concentration being far higher than in blood [1]. At these springs the gradient runs the other way: the water holds a fraction of what is already in your blood.

Ayer Hangat in Langkawi is the outlier. The same study measured 13,832 mg/L chloride, 7,905 mg/L sodium, 947 mg/L sulphate and 394 mg/L magnesium. The spring is about 2 km from the open sea, and the authors suggest the water is a mix of seawater and groundwater. Their sample came from a narrow man-made well about 1 m across, not a bathing pool [9].

Two caveats. These are samples from one study at one point in time, and mineral content can shift with rainfall and with how a pool is fed and drained. And for most other springs on this site, including the salty Tingkayu spring in Sabah, we could not find any published magnesium figures.

Who should be careful

Magnesium itself is unlikely to be the problem in a hot spring. Heat and fluid loss are the bigger issues.

• Kidney disease. Dangerous magnesium build-up in the blood is rare and mainly seen with severe kidney failure or medical overdosing [1]. Soaking has not been shown to cause it, but if your kidneys are impaired, ask your doctor before using any magnesium bath salts, flakes or sprays.
• Heart conditions and blood pressure. In the Bath spa study, two hours sitting in 35°C water raised the heart’s output (cardiac index) by about half and doubled urine output [4]. Many Malaysian pools run hotter than 35°C. If you have heart disease or take blood pressure tablets or diuretics, keep soaks short and drink water.
• Early pregnancy. In a study of more than 23,000 pregnancies, hot tub use in the first trimester was linked to about 2.8 times the risk of neural tube defects [10]. Skip long, hot soaks in early pregnancy and check with your doctor.
• Broken skin, eczema or psoriasis flares. Damaged skin lets minerals through more easily than intact skin [6]. Salty spring water is a different exposure from a low-mineral pool, so start with a short dip.
• Anyone tempted to drink it. Water from Sungai Klah and Ulu Slim tested at 0.07 and 0.03 mg/L arsenic [9], above the WHO drinking water limit of 0.01 mg/L [11]. Soak in it, don’t drink it.
• Anyone treating a magnesium deficiency. Don’t swap a prescribed supplement for soaks or sprays. The 2017 review called that kind of swap alarming [1].

What this means at Malaysian hot springs

If magnesium is your reason for going, the popular inland springs won’t deliver it. Sungai Klah, Dusun Tua and Sungai Serai are low-mineral water, and their appeal is the heat, the setting and the time out.

Ayer Hangat in Langkawi is the only Malaysian spring where we found published data showing substantial magnesium [9]. It was closed for redevelopment as of 2026, so check its page before going. Even when it reopens, its water holds under a third of the magnesium in seawater, and no study has tested whether soaking in it changes anyone’s magnesium levels.

Ulu Slim tested highest of the inland springs at 0.8 mg/L, but its water came out at 90°C at the sampling point [9]. It’s a place to look at, not bathe in.

Rinse off after a soak if the water is salty, and use a moisturiser if your skin tends to dry out.

So is it worth soaking for magnesium?

Hot spring water is not a magnesium supplement. Healthy skin lets through very little magnesium, the best-controlled human studies found no rise in blood levels, and most tested Malaysian springs contain less magnesium than your blood. There is early evidence from one small study that magnesium-rich salt water can help dry skin from the outside. Go for the warmth and the setting, and get your magnesium from food.