Concerned about my cat's red "bum"

I just noticed that my cat's "bum" is quite red. I don't see any blood in his stool. I tried to wipe his bum with a baby-wipe to see if any red would come off on it, but he make a slight crying noise and won't let me near the lower part of his tail and bum. He is eating and running around as usual. I don't know if it is blood (as in coming out of his bum), or just irritation of the anal tissue. Does anyone have any ideas? I'm going to call the vet tomorrow.

Note: he is a 2 year old, neutered male.

Thank you.

He might have plugged scent sacs.
He needs to be seen by your vet ASAP for a diagnosis.
You do not want to wait.
He might be very uncomfortable or in pain.

Cats can get blocked anal glands from time to time. It's also a common problem in dogs, and both are sometimes known to do the same thing to help alleviate it -- drag their bottoms along the carpet. You can go to the vet to have the anal gland expressed, or you can get it done at a groomer's, or you can do it yourself. Since your cat is already showing a red bottom it might be a good idea to get the vet to take a look at him, but if they have to express the anal gland you might want to get them to show you how to do it yourself in case you have to do it next time. It might save you some money in case it needs to be done often. Just be sure to keep a box of latex gloves on hand cause nobody likes doing it bare-handed.