If your hair is long enough to reach the bathwater, it is normal to tie it up before getting into an onsen. For people with long hair, a hair tie is almost an essential item.
Even after washing your hair, tie it up before getting into the bath. You can make a bun or simply tie it so that most of your hair stays out of the water.
That does not mean that a single strand or the very ends of your hair touching the water automatically makes you rude. If your hair is clearly tied up and a few ends happen to touch the water, most people will not consider that a serious problem.
What matters more is showing consideration for the fact that the bath is shared with other people.
On the other hand, if someone enters the bath with long hair hanging loose and spreading across the surface of the water, many Japanese people would see that as poor manners. It may not be serious enough for a stranger to confront you directly, but that does not mean nobody minds. People around you may still feel uncomfortable.
You might wonder, “But I just washed my hair, so isn’t it clean?” The point is not whether each person’s hair is actually dirty. In a shared bath, keeping long hair out of the water has simply become part of the expected etiquette.
There is no rule saying that hair must be tied up once it reaches a certain number of centimeters. The practical standard is simple: if your hair is long enough that it is likely to reach the bathwater, tie it up.
Forgetting a hair tie can be surprisingly inconvenient. If you forget one, you can use a towel to help keep your hair up and out of the water. The towel itself, of course, should not be put into the bath.
Onsen etiquette is not about creating a perfect hairstyle or making sure that not a single strand ever touches the water. The important idea is much simpler: this is a bath everyone shares, so show that you are being considerate of the people around you.
