Black Stuff on Cat's Chin

My cat's chin has this weird black stuff on it. I have tried wiping it but it does not come off. I am not entirely sure where he has been.
When I touch it the area feels hard, but the cat doesn't seem to be in pain. However, he hasn't been eating, he's lost weight, and I've noticed some hair loss around his legs.

[Cliff Redford, DVM]

Two separate issues likely. The chin lesion's sound like "chin acne". High school stress can cause this :) Keeping it clean with an antibacterial soap will help but it is not serious...except for one's social life.
The weight loss, anorexia and hair loss is much more of a concern. These signs are very vague in the sense that many diseases and conditions come with these signs. An examination by your veterinarian will be necessary and they will likely recommend some laboratory tests to assess organ function.
Good luck.