Acidic hot springs, such as those you find here in Kusatsu, are strong enough to kill bacteria and have a high medicinal content, so you can bathe quite safely. People from high risk groups bathing in hot springs that do not have this germ-killing power may run the risk of contracting infections. (High risk groups include alcohol drinkers, smokers, atopy sufferers, children, the elderly, sufferers of chronic diabetes and chronic obstructive lung disease, people with impaired immune systems and those recovering from surgical operations). In our opinion, acidic hot springs are the best and safest to use.
Kusatsu Hot Spring is a hot spring containing highly acidic hydrogen sulfate alums and copperas. It kills bacteria very effectively, so it is totally safe to bathe in.
Please note that soap cannot be used in acidic hot springs.

Legionnaire's bacteria lives naturally in soil and freshwater and there is a danger that this pneumonia-causing bacteria may get into such hot spring water. Legionnaire's bacteria flourish at PH7 in conditions of about 30-42℃. High risk groups are at particular risk of picking up the bacteria, so they should avoid places where the water is reused, or the quantity is low. Places that produce bubbles (i.e. Jacuzzis) are a virtual playground for bacteria and therefore are particularly dangerous. The indoor spread of bacteria due to air conditioning equipment occurs in the same way. (The disease originated in a military legion and that is where the name comes from).

１． Avoid large communal baths.

The worst possible situation is a large public bath with no bacteria-killing power, where the water is reused and is provided in low quantities. This sort of place is literally a breeding ground for bacteria. If you bathe here, you should rinse off all water thoroughly in the separate shower. It may seem repetitive, but even if one bubble remains then you may be at risk. Wash carefully, and then leave the place as fast as you can. However, not all large baths need to be avoided. If there are a few reasonably sized bathtubs that do not appear too big, and if each one is fed individually with clean spring water, then it is possible to use them safely.