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If you walk into a pharmacie in France, you’ll immediately bump into a giant display of thermal water spray cans. A whole host of French skin care brands like Avène, La Roche-Posay, Uriage and Vichy sell thermal water sprays. What is it, what’s in it, what does it do and how is it different from regular water?
What is thermal water?
Thermal water comes from hot springs. The water in these hot springs come from deep in the ground, where it’s heated by geothermal activity (the Earth’s natural heat which also causes lava to be molten).
What’s in thermal water?
It’s mostly water, of course, but it isn’t “just water in a can”! As the thermal water rises to reach the spring, it passes through rocks and soil which dissolve to add minerals to the water. The mineral content of a particular thermal water depends on where it comes from. The minerals include the ones found in your skin’s natural moisturising factor (NMF), like chlorides, sodium, potassium, calcium, and magnesium.
Here are the compositions of the 4 most popular thermal waters (source: Bacle et al., Int J Dermatol 1999, brand marketing materials). There’s some variation between batches of course, since it’s a natural mixture.
|Composition (mg/L or ppm)||Avène||La Roche-Posay||Vichy||Uriage|
|Total dry residue||207||444||5120||11000|
As you can see, the composition varies a fair bit, with Uriage, the thermal water with the highest mineral content, being 55 times more concentrated than Avène, which has the lowest mineral content.
“-” in the table means no data, since different thermal water brands like to highlight different aspects of their water. La Roche-Posay talks a lot about the selenium content of their water, while Uriage emphasises the high calcium concentration. Avène talks a lot about the 2:1 ratio of calcium and magnesium in their water.
There’s also nitrogen gas inside the can that acts as a propellant, to push the water out as a spray. Paula’s Choice writes that the nitrogen “can generate free-radical damage and cause cell death”, which luckily isn’t true, since nitrogen gas (N2) make up 78% of the air we breathe! It’s actually very unreactive, so unreactive that it’s commonly used in laboratories to flush out more reactive things like oxygen and water. (The papers cited in the Beautypedia article actually involve chemicals that just contain nitrogen atoms, not nitrogen gas itself.)
What does thermal water do for skin?
There are a handful of peer-reviewed studies that show that thermal waters have beneficial effects. Unfortunately, almost all of them are performed by the companies themselves, and naturally they show that their product is better than the others, so they should be taken with a grain of salt. (It’s kind of unavoidable though – independent scientists aren’t going to get funding for studying water when there’s cancer to be cured and climate change to undo.) The two best-studied thermal waters are Avène and La Roche-Posay. While this doesn’t necessarily mean that their products are better, it does mean that their effects are more substantiated, for now.
A lot of the studies are also in vitro, which means they’ve put bare cells or tissues in thermal water and watched the effects. These studies are good for seeing how a product works, if it works – but they’re not so good at telling you if it works in then first place. Humans are much more complex than a handful of cells in a petri dish.
With these caveats in mind, here’s what the studies say thermal water can do:
Protect from UV damage
La Roche-Posay, Uriage and Avène thermal waters have been found to protect cells from UV-related damage in vitro. Additionally, mice treated with a cream containing La Roche-Posay developed tumours slower than control groups after UVB exposure. A La Roche-Posay thermal water cream also reduced the formation of sunburn cells in human volunteers after UVB exposure.
It’s been speculated that selenium, zinc and/or copper are responsible for this effect, since they’re important for the functioning of antioxidant enzymes naturally in the skin, which soak up the damaging free radicals produced by UV light.
Thermal water is commonly used for a lot of conditions related to inflammation, including atopic dermatitis (eczema), psoriasis, and ichthyosis.
In vitro, Uriage, La Roche-Posay and Avène water decreased the production of inflammation-causing chemicals by skin cells. A study with human volunteers found that a La Roche-Posay thermal water gel decreased irritation caused by sodium lauryl sulfate.
A clinical trial found that Avène reduces the severity of atopic dermatitis (eczema) when added to a cream, and decreased the amount of inflammation-causing bacteria on the skin. Avene also reduced the severe peeling that’s usually a side effect of using tretinoin as an acne treatment. La Roche-Posay also managed to help 50% of a clinical trial group suffering from psoriasis, although that study involved drinking the water as well as applying it on the skin.
You’d expect that a higher mineral content might work better, but interestingly, comfort, softness and suppleness are better with a lower mineral content, and irritation is lowest (it’s worth noting though, that this particular study was performed by the parent company of Avène, the lowest mineral content water).
S Seite, Thermal waters as cosmeceuticals: La Roche-Posay thermal spring water example, Clin Cosmet Investig Dermatol 2013, 6, 23–28.
C Merial-Kieny, N Castex-Rizzi, B Selas, S Mery & D Guerrero, Avène Thermal Spring Water: an active component with specific properties, J Eur Acad Dermatol Venereol 2011, 25 Suppl 1:2–5.
I Bacle, S Meges, C Lauze, P Macleod & P Dupuy, Sensory analysis of four medical spa spring waters containing various mineral concentrations, Int J Dermatol 1999, 38, 784–6.
F Beauvais, JL Garcia-Mace & F Joly, In vitro effects of Uriage spring water on the apoptosis of human eosinophils, Fundam Clin Pharmacol 1998, 12, 446–50.
Thermal waters from Avène and Uriage were press samples, which did not affect my opinion. For more information, see Disclosure Policy.