There hasn't been a lot of longterm research. Effects will also vary by frequency, intensity, etc. Some frequencies can cause heating, which is a problem for so

There hasn't been a lot of longterm research. Effects will also vary by frequency, intensity, etc. Some frequencies can cause heating, which is a problem for some areas like the eyes. Some frequencies increase glucose metabolism for the cells affected. No idea what that does longterm, but theoretically, that could create an environment for cancer growth.