Are you ready for some beauty science?

Let’s start with a repost of a comic about Tamatsukuri Onsen, one of Japan’s original beauty onsen, a downright fountain of youth according to the Chronicles of Ancient Izumo.

I’m going to preface this by saying I’m not an expert. I just really like going to onsen and have picked up some nerdy knowledge and onsen guides here and there. I am not a chemist or a beautician. I can say, however, that I have noticed some changes in my skin quality over the course of my time in Shimane, which, for the past few years, have been ranked #1 for beautiful skin based on its humidity, hours of sunlight, life habits, and other environmental factors. I didn’t really believe this over the course of my first winter here when I had terribly dry skin due to indoor heaters, but when I started thinking skin care in terms of texture rather than acne (or lack thereof), I found that following skin care advice I’ve heard here really works well.

But beyond that, knowing nerdy things about onsen I enjoy anyway is plain fun. So let’s dive in! (No. No diving at the onsen. Don’t be Faux Pas Man.)

Onsen, which are all at least 25 degrees C at their source and contain at least one of 19 designated chemical elements, can be categorized in some of the following (sometimes scary-sounding) ways:

Simple onsen (単純温泉: tanjun-onsen)
The most common type of onsen found throughout Japan, with relatively low concentrations of chemical elements (general 1g/kg and below). Good for people with sensitive skin.

Hydrogen carbonate onsen (炭酸水素泉: tansansuiso-sen)
Good cleanser and for giving you smooth skin.

Sulfate onsen (硫酸塩泉: ryuusan’en-sen)
Works like a toner and supplies moisture to skin.

Iron onsen (鉄泉: tetsu-sen)
Water with somewhat light brown color, good for people prone to anemia.

Chloride onsen (塩化泉: enka-sen)
Helps your skin to retain moisture and gives it a damp texture (in a good way).

Sulphur onsen (硫黄泉: iou-sen)
Antibacterial properties make this good for treating skin ailments. Also considered good to detox your system, and for helping your skin retain moisture.

Radioactive onsen (放射能泉: houshanou-sen)
Includes things like radium onsen and radon onsen. Good for pain relief.

Carbon dioxide onsen (二酸化炭素泉: nisankatanso-sen)
Basically, carbonated onsen. However, the gas bubbles are too tiny to see. Said to promote blood flow, these are relatively rare in Japan. (Shimane has one in the little town of Iinan, named Ramune Onsen. Gee, I wonder how it got that name.)

These chemical elements should be indication on a sign somewhere around the onsen, based on how much of them can be found per 1kg. Just because these are the primary chemical elements which any given onsen might be known for, it doesn’t mean they’re limited to those characteristics.

You also want to note the onsen’s pH balance. Onsen with pH balances from around 6 to 7.5 are the gentlest to your skin. Alkaline, particularly 8.5 and above, are supposed to be good cleansers. Higher acidic concentrations are good for their antibacterial properties (but always remember to keep hygiene in mind when visiting an onsen!).

If you’re looking for beautiful skin, you also want to keep an eye out for metasilicic acid (メタけい酸 metakeisan) content. H2SiO3 is a very simple, diluted silicic acid thought to stimulate collagen, which is what gives your skin a springy, youthful texture (in other words, it prevents wrinkles). Back to that Tamatsukuri Onsen comic up there, the joke is that when the onsen was introduced in writing about 1,300 years ago, the research team found all the locals partying in the hot springs, young and old alike. All of them had youthful, springy skin. Nowadays, onsen aficionado attribute this to the high concentration of metasilicic acid, at 110mg. In order to be considered a good beauty onsen, most would aim to have at least 50mg.

I mentioned that in Japan, people think of skin care in terms of texture (or whiteness, but that’s a totally different topic). They have a number of fun words to describe what skin should feel like, many of which don’t have a full equivalent in English. Some of the common ones are:

つるつる tsuru-tsuru: slick and smooth
すべすべ sube-sube: smooth and sleek
ぺたぺた peta-peta: skin moist enough to make a little sound when you lightly press your fingers to your skin
うるうる uru-uru: damp, moist, well-hydrated skin
さらさら sara-sara: silky and soft
もちもち mochi-mochi: a springy texture (yes, like a good rice cake)
しっとり shittori: retains its moisture really well

Or at least, if I had to try really, really, really hard to differentiate between things like uru-uru and shittori this is my sense. I’m not a professional linguist either, I just happen to be mostly fluent in Japanese. And I do like gitaigo (or gi’ongo, in peta-peta‘s case?).

And I like onsen. That too.

Hopefully this will help to make your next visit to an onsen more interesting. Throw these terms into conversation with your friends, and then make up observations about the smell and color and feel of the onsen water and pretend you’re taste-testing on a food competition show or something. Your friends will either think you sound really cool or they will be tempted to dump a bucket of cold water on your head to make you just shut up and enjoy onsen for the simple pleasure that they are.