Acne is a skin disease which occurs when oiliness and dead skin cells clog the pores.
Mild acne is characterized by few red dots while in more severe cases the dots can be hundreds and cover the face, neck and back.

The dots can be big, dense and painful (cysts ).
It commonly occurs during puberty, but it can occur at any age. Some women who did not manifest acne at their puberty can manifest it in their adult life.