Why is my right thumb numb?

Numb thumb: There too many possibilities to discuss in 400 characters. The nerve pathway goes from your brain through your neck and down your arm to your thumb. The problem could be anywhere along the way. It could be as simple as pressure on the digital nerve from sleeping the wrong way to a brain tumor. If you are concerned i suggest you get it looked at by a physician.

More information..: It is hard to speculate without more information: are any other fingers numb? Did you have an injury? How long has this been present? Does anything make it better or worse? Is it associated with any weakness? You really need to have an examination to get an intelligent answer. Good luck!