An imbalance between new and dying skin cells causes the flakes on your dog's coat and this aspect of skin peeling.
There are two forms of seborrhea: oily (oleosa) and dry (sicca). A combination of both is frequent. A change in the amount and quality of the oily skin secretions (sebum) caused seborrhea.
Underlying disease such as allergies, endocrine disorders, dietary deficiences are frequent. These conditions cause an imbalance of the skin's ecosystem leading to secondary seborrhea.
Primary (inherited) seborrhea also exist. It affects young dogs of certain breeds including Westies, Dachshunds, Labrador Retrievers and others. In Shar Peis, primary seborrhoea is common in the body folds.
Oily skin exudes a waxy, greasy substance and you may see comedones. Often, dogs smell bad due to this excessive production of free fatty acids which gives a characteristic odor of "rancid butter".
With dry seborrhea, dandruff are more frequent and a lack of sebum irritates the skin. Skin hyperpigmentation and hair loss are also common.
The damage of the natural protective skin barrier can be a favourable place for bacterial or yeast infections. Itch may appear too. The ears or the tail ('stud tail') are sometimes affected or only a part of the body.
Stud tail is an overactive sebaceous gland on the upper part of the tail. This gland produce sebum but also pheromones included in territorial marking and sexual communication.