Plastic cat utensils are easy to hide dirt and accumulate bacteria. When the cat's chin, mouth, and nostrils touch the surface of the bowl, the bacteria will transfer to the cat's skin, which can easily cause black chin. The black chin caused by this reason will generally improve after replacing it with stainless steel tableware, porcelain tableware, or glass tableware, but it should be cleaned more.
After cats have sexual maturity, if the sexual hormones in their bodies are secreted too strongly, it will cause endocrine disorders in the body. The reaction on the skin is folliculitis. This type of male cat is more likely to occur than female cats, and it is more common in the tail and chin. After sterilization, it may help the black chin improve, but it is not absolutely true.
Cats have too high oil content. Now there are most sayings that eating too oily cat food will cause black chin. I have found a lot of information and talked to many cat friends. There is no strong evidence to confirm it. I personally believe that eating too oily cat food may cause black chin due to individual differences in cats. So you can try to verify whether your cat's black chin is caused by cat food by changing the food.