Reasons for black stuff on a cat's mouth:
1. Clogged hair follicles may be caused by hormonal imbalance in cats. Also, the chin is an area that cats cannot clean themselves. The oil secreted due to hormonal imbalance can clog pores, resulting in black stuff.
2. If a cat's diet contains too much cat fat, it can also cause clogged hair follicles and the appearance of black spots.
3. The cat's food bowl is not clean enough. Plastic water and food bowls have a low density and many small holes that are hard to see. These small holes harbor bacteria that are difficult to clean. Using plastic food bowls can cause the cat to be infected with bacteria, resulting in black stuff on its mouth. 
How to fix black stuff on a cat's mouth:
1. If a kitten has black residue on its chin, it is likely folliculitis. It needs to be cleaned with saline solution and treated with medication containing antibiotics such as erythromycin.
2. During treatment, the hair on the chin area needs to be trimmed with scissors to make it easier to clean the black foreign matter. Then, disinfect with diluted hydrogen peroxide, and finally apply an antibacterial and anti-inflammatory medication.
3. In addition, you need to replace the cat's food with low-fat and low-salt food and provide enough drinking water.
