Redness and itching on arm pit and inner thigh

Hey vets, my dog is two and has extreme redness on inner thigh and under arm pit it does itch him. What could it be and how can I help him? 

Hello and thankyou for this excellent question.  That skin is in a deep fold and although skin folds aren't a cause of itching, the heat / moisture under there can create a cosy environment for microorganisms such as yeast to multiply and have a party.  Particularly when skin is damaged, they like to get involved.   So what could have damaged the skin?  I wonder about allergy, local joint pain causing licking, a foreign body, internal pain such as pancreatitis (for some dogs the armpit is a convenient spot they can reach), also endocrinopathies (a set of hormonal diseases).  This case looks painful.  Looking at it, I'd suggest that the moment for home treatment has passed.  Your vet will try to a) ease the symptoms and b) address the causes.  Wishing you both all the best.

Ps your vet may also test for eg yeast over growth and will often only treat if they feel it is necessary - rereading my first answer, it rather sounds as if I can diagnose one by looking but I cannot.