I've been grooming my dog of her undercoat to help shedding and I've gotten to the worst part, the tail bone, right behind the tail at the rear of her back. The rest of her fur and skin looks great but this area, when I brushed under her top fur and pull the fur up to get at it really good I noticed a lot of flakes that weren't there before I started going under her fur. There were no knots there, just thick fur. She is a med/long haired mixed breed senior dog and I don't know if it is just really hard for her to clean this area. I bathe her probably once a month and the rest of the time just put her in the bath and get her feet if it is rainy and her feet get dirty. I use the oatmeal bath shampoo usually with conditioner. I've never noticed this on her before and this is the only part of her body with this problem.