tumors tend to be bigger. and ingrown hairs tend to have hairs in them (you can usually see them just under the surface of the skin).
tumors tend to live farther under the surface of your skin than ingrown hairs would. they are hard knots that you can feel, whether in breasts, testicles, or in the fat of your wrists.
if in question, have your doctor look at it.
I bust my arse so that I can get somewhere in life, so why am I not there yet?