Will there be any health issue if I use cellphone for a long time where reception is bad

I feel that my cellphone heat up very rapidly when I was on go bus, where signal is not that elegant.

I am wondering if I use cellphone to make a lot of calls on a bus or in the basement, would there be any health issues?

Or if not health issues, how to prevent my cellphone to be overheated when cell phone reception is bad?