Did it start off as a hot spot and because of constant licking has turned black ( a little scaly) ? Well my Samson had this due to some allergies he started constantly licking himself, his pink skin turned black! But with some oatmeal, antifungal antibacterial shampoo it is going away! THANK GOD! Cause it really freaked me out! I Wash him every two days and have seen a significant difference in 1 week, also FYI. His diet might be to blame if he is darting at whatever falls under the dinner table then he maybe getting stuff he is not supposed to be eating ( or on his dog food) ive cracked down on what sam eats and doesnt and no more weird spots with no hair ( hair still in process of growing back but its on a positive turn around!!! ) try it!