Cats shed their coats seasonally, depending on the hours of daylight they're exposed to each day. Winter means shorter days and longer, thicker hair. But what happens if your feline friend is losing his hair? Anna M. writes:
Anna, hair loss in cats can be caused by a number of things. Foremost is diet. A cat who is either not being fed enough protein or is being fed an inadequate type of protein will certainly experience hair loss. It's important that all cats be fed a high-quality, wet-food-only diet which consists mostly of meat. You can see our food recommendations in this post.
Another potential issue is skin allergies. Verifying this will require a visit to your veterinarian. He or she can also recommend a course of treatment. If you haven't taken Michael to the vet in a while, this could be the signal that it's time to get him a checkup.
Lastly, some cats chew their own hair off in patches when they're stressed. You mentioned that Michael and your other cat, Luna, don't get along. It's possible that this is stressing him out to the point where he over-grooms himself. This usually makes cats feel better in the short term, but can also become a knee-jerk reaction to long term stress. We have a post on the subject here. We also have a good post on helping your kitties get along here.
We feel that with a little effort and some good nutrition, you can help Michael with his hair loss. We wish you both all the best!