Lab skin problem

Question
This morning I noticed my 10 month old black lab had a patch of matted fur on his back at the base of his tail. I gentley separarted the fur to find what looks like a 6" by 10" area of infected skin. The skin is red and blotchy with yellows coming from below.
This may not have anything to do with this condition, but several days ago his was favoring one of his hind legs and very uncomforatable for 4 to 5 hours
What is this and what can I do about it?

Answer
This sounds like a hot spot or acute moist dermatitis.  It could be caused from an injury.  The best thing you can do is to shave the hair off of the affected area and wash it daily with soap and water.  Take the dog to the vet if it does not dry up after a couple of days.