Your cat probably won't develop a skin problem if you feed it a good diet, brush it frequently, and let it groom itself naturally. Some cats, however, are susceptible to allergies that can cause them to scratch, bite, and lick at themselves constantly. Eventually, this can result in hair loss or even open sores unless the condition is treated. Fleas are the most common cause of skin problems. Even a single fleabite can set off allergic reactions in a cat. Most of the once-a-month flea treatments from your vet have been shown to be highly effective. Flea collars don't work as well, and some cats actually show allergic reactions to the chemicals they contain. If your cat has another allergy, such as to a particular type of food, you'll have to consult with your vet to develop a program to monitor its diet until that food is identified. Other skin problems that can affect cats include acne, sun damage, and mites. Consult your veterinarian if you notice your cat scratching frequently or experiencing any noticeable hair loss.