Your skin type is determined by genetics. There are four basic types: normal, dry, oily & combination skin. Oily skin is skin that produces too much sebum, the sebaceous glands are overly active: we then speak of hyperseborrhoea. Sebum production is excessive in the hair follicle & we observe an imbalance between water & lipids in the hydrolipid film.
We recognise oily skin because it is characterised by shine, enlarged pores, blackheads, whiteheads or occasional red spots & a dull complexion all over the face. When the signs of oily skin are for the most part located along the centre of the face, known as the t-zone (forehead, nose & chin), we then speak of oil-prone combination skin.