Certain diseases in dogs can lead to an overproduction of skin oils (seborrhoea) and thus to a greasy coat. Similarly, fungal infections can cause the dog to lose some of its coat. Most of the time, however, our dogs have coat problems, which are mainly noticeable in the form of increased dandruff or a dull coat. Dandruff is the smallest dead skin cells that have been renewed and are usually not noticeable at all.
Basically, dandruff is completely normal, as long as it does not get out of hand. However, dry air, insufficient coat care, poor nutrition, a metabolic disorder or psychological problems can trigger increased dandruff. Similar reasons come into question when the coat becomes increasingly dull. This should not be dismissed as a "blemish", but should be a clear indication that something is wrong with the four-legged friend.