No one knows the reason why, but seem to guess that it's to save money in the public restrooms (both the cost of soap and of water). And a lot of Japanese homes have (or used to have) the toilets with the faucet on top and (for some reason) you wouldn't want the hand soap to run back into the tank.

In Japan, it is common to find public restrooms—especially in older train stations or public parks—that do not provide soap or hand towels. This stems from a historical "design code" for public facilities where soap was not considered a mandatory requirement, and many locals carry their own "tenugui" (hand towels) and pocket soap or sanitizer. Additionally, there is a cultural emphasis on personal responsibility for hygiene; many Japanese people feel more comfortable using their own products than shared ones. Another reason is the design of some traditional sinks; for instance, you should never use soap in the small sinks located on top of toilet tanks, as the residue can damage the internal flushing mechanisms. However, this is changing; modern department stores, major train hubs, and newer public buildings almost always provide soap dispensers. For travelers in 2026, the best advice is to carry a small bottle of hand sanitizer or paper soap strips to ensure you are never caught unprepared in a more traditional facility.