There is a condition called alopecia areata, which produces bald
patchesAllergy testing
Skin color - patchy. Although most attnetion is paid to scalp bald
spotsBirthmarks - pigmented
Liver spots
Measles, koplik spots - close-up
Mongolian blue spots, this can in fact happen anywhere on the body. The hair often grows back eventually, but treatments don't help much. After all this time, I doubt anything will regrow. For definitive diagnosis, you should see a dermatologist, but it's unlikely there are any health implications, or available treatments.
Best.
Dr. Rockoff