The main reason people remove their shoes in Japanese homes is simple: they do not want to bring outdoor dirt inside.
In Japanese homes, people may sit or lie on the floor, and children often play there. The floor is not just something people walk on. It is also part of the living space and often comes into direct contact with the body.
Because of that, walking into the house in shoes that have been worn outside feels very dirty to many Japanese people.
The entrance, or genkan, marks the boundary between outside and inside.
The area where shoes are removed is physically inside the building, but it still feels like part of the outside. Only after removing your shoes and stepping up into the hallway or living area does it feel as though you have truly entered the home.
If someone crosses that boundary in outdoor shoes and takes even one step onto the hallway or room floor, many Japanese people will feel a strong sense of discomfort. It does not feel like a minor breach of etiquette. It feels as though dirt from the street has been carried directly into the living space.
What matters is not simply going through the motion of taking off your shoes.
Even without shoes, walking around in badly soiled or sweaty socks can still feel unhygienic to the host. The real concern is whether you are entering the home in a reasonably clean condition, not just whether your shoes have been removed.
When visiting someone else’s home, clean socks are generally a better choice than bare feet. Bare feet are not always considered rude, but socks are often seen as more considerate because they prevent sweat and skin oils from coming into direct contact with the floor.
If slippers are provided at the entrance, it is natural to wear them. If there are no slippers, however, walking around in clean socks is perfectly acceptable. Slippers are not required in every Japanese home. The safest approach is simply to follow the household’s usual way of doing things.
When a foreign visitor does not know the custom and starts to enter with shoes on, someone will normally stop them immediately. Not knowing the rule is not a problem by itself.
However, ignoring the request to remove your shoes and continuing inside is a different matter. It can look as though you do not care about dirtying the person’s home, and the host may never want to invite you back.
People in Japan do not remove their shoes merely because it is an old custom or a formal rule of etiquette.
They remove them at the entrance to keep outdoor dirt out of the home and keep the floor clean as part of the living space.