Are there any bald spots at all? Is this a long haired or short haired cat? How long has he been doing this?
There are a number of reasons that cats will shed abnormally. Some of them include hyperthyroidism, cushing's disease, mange, ringworm, and many more. Here is a link to a page with a chart describing different causes of hair loss to help you narrow it down since you can see your cat and I can't:
To get a definite diagnosis you will need to take him to your veterinarian. It is possible that your cat is just shedding excessively with no underlying cause, but if he were mine I'd like to rule out the possible medical problems for sure.
If you have further questions let me know. If you find this answer helpful please click accept. Thank you.Lynn