These glands release oils which protect the mammal's fur and hair. This serves multiple purposes. One effect of this is it makes the animal look larger than it really is. Another reason for the erector muscles, is when the hair stands on end, it provides for better insulation. There are two types of hair, definitive and agora.
Definitive hair grows to a certain length and then ceases to grow anymore.
Angora hair on the other had, will continue to grow until the hair falls out. There are three categories of hair which fall under these types. The first type is guard hair. Guard hair gives the color and the shape of the animal. Guard hair can come in spines, stiff and definitive like in porcupines , bristles, long, firm, and angora like a horses mane, or guard hair can be awns, definitive, narrow, and weak at the base.