Why Do I Get Numbness On Face After Using Cell Phone?

Health Issues with cell phones. 45 year old male. the past two weeks when using my cell phone (a small razor phone) for over 20 minutes holding close to face where it contacts skin) I have noticed that right side of my face gradually starts to tingle and go numb. The effects last for several hours then gradually goes away. I notice that it only occurs when I use the cell phone. mp