black patches in arm pits

Question
My dog has black thick patches under his arms that remind me of what horses develop.  what is this and what do i need to do to make it go away or is it okay?

thanks so much!!

Answer
When I have seen this it is from a yeast infection on the skin - it needs to be treated by a vet before it gets bad and spreads or gets sore.  I have seen some skin discoloration before but it is minor and not raised at all - if this is in thick patches, go to your vet please.