My cat has black patches on his stomach. What's the best treatment?

Hi, and thanks for your question.
Even though a picture would help to understand better the underlying cause, This presentation could be due to a trauma or localized spot of skin infection (likely to be caused by bacteria or mites). A check up, appropriate disinfection and possibly antibiotics (oral, topical or in a shampoo formulation) are needed to solve the problem.
Disinfection may be started at home with very diluted hibiscrub or betadine or salted water baths. Buster collar may be useful as well to avoid any licking.
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