red bottom

So this is random, When a cat goes to the kitty box as pushing out a poop about 3mm of red flesh is on show. My vets seem to think this is normal as he’s bald “you can see more because he’s nude” it always goes back in. Is this common?

Madeline looks like she has a diaper rash-Have any of you dealt with this? It doesn't look horrible but it is red and I do not want her uncomfortable. Besides keeping it clean, Is there anything I should be putting on it? #PoorBaby