New mark on dogs behind

Hi. My dog Oliver is 9 months old, lab/hound mix that we rescued as a puppy. He has no history of skin rashes or issues with his coat of any kind. No medical history to really speak of. we went on vacation and he went to a boarding camp for a few days. We picked him up and he has this bare patch on his hind quarters. It’s below his anus and to the left. He doesn’t mind me touching it, he doesn’t lick, scratch, or bite at it either. When I first saw it there was some feces stuck to the side of it. When I cleaned it the hair the feces was matted to pulled right out and again he didn’t seem to notice. any ideas what this could be? 

Hello!  Anal skin is delicate and very prone to infection, especially in the presence of itching (eg in the case of allergy) or lots of bacteria (introduced by the poo), or anal gland itching, or an anal skin fold that produces a haven for bacteria.  This might have been the perfect storm.  We would advise seeing a vet to get proper treatment underway;. This may involve anti-itch / anti-inflammatory treatment and antibiotic or antiyeast, depending what bugs are hanging out there.  Best of luck and please let us know how you get on!