That winter I also tried several prescription creams for my rosacea, and while they helped in the short run, they caused flare-ups over time. At that point, I’d somehow bought into the idea that spraying French water on my face would help. After all, I’d installed a water filter in my shower and started using a humidifier. The more moisture in the air surrounding my skin, the better, right?

But just like the idea that drinking water is good for your skin, this just might not be true. The practice of spraying thermal water on one’s skin likely comes from an ancient Greek tradition called balneotherapy, or bathing in mineral water baths as a dermatologic treatment. These days, the practice blurs the lines between a spa experience and an alternative medical treatment. The science behind spraying thermal water is mostly backed by studies done by the French companies that sell the products. One 2015 study by a group of German researchers at Goethe University in Frankfurt found that spa waters can help in the treatment of chronic inflammatory skin diseases, but it called for further study. “A general problem of studies dealing with spa waters is that most of these studies are initiated by the spa water manufacturers themselves. Independent scientific investigations are rare and necessary to providing a more solid basis to evaluate spa water-mediated effects … Particularly in the last few decades, the French cosmetic industry has marketed thermal spa waters as cosmeceuticals, requiring some effort to prove cellular effects.”

In fact, the sprays can actually backfire. “It does help with moisture, but it's important not to apply it too many times during the day because too much water can be drying. It's a very fine line, unlike the creams and moisturizers that are emollients and are a bit thicker, with thermal water, it's important not to spray it multiple times because it can create the opposite effect,” explains Emma Guttman, a dermatologist at Mount Sinai Hospital in New York and the director of the Center of Excellence in Eczema. "If the body is in too much contact with water, it actually dries. It's like washing your hands multiple times during the day—your hands will be very dry."

Another dermatologist, Annie Chiu at The Derm Institute, a dermatology practice in Redondo Beach, California, said that while the potential healing powers of thermal-spring water are understudied, there might be benefits. “Thermal-spring waters usually have a unique mix of minerals that contribute to the overall health of what we call the skin biome. The skin essentially has a complex ecosystem with a delicate balance of minerals, fatty acids, and even good bacteria,” explained Chiu. “If you wash your face with harsher soaps or in general have more inflammation on your skin due to a skin condition like acne or rosacea, a thermal-water spray could theoretically rebalance this micro environment for a healthier skin barrier.”