On average, the pores on the face of someone with oily skin produce around two grams of sebum a year.

Characteristics of oily skin

The thin layer of oil this creates on the skin leads to a

• shiny surface,
• open pores (which stretch as oil accumulates in them),
• blackheads (which occur when that oil is exposed to air and oxidizes) and
• whiteheads (which occur when dead skin cells stick in the oil and degrade).

Sometimes the pores create acne too, but don't assume that if you have oily skin, acne follows - research seems to show that the oil in acne-prone skin is thicker and more likely to clog the pores than normal.

There are various reasons for oily skin. It's often hormonal, which is why teens are prone or why skin can become oilier before your period; it can also be triggered by high humidity.

Finally, oily skin can actually be caused by poor skincare. If you strip the top layers of the skin of too much moisture, the lower levels produce more oil to counteract this. On skin which produces higher oil levels anyway, this leads to serious shine.