T-Zone skin is also often referred to as Combination skin, meaning that the people in this grouping have more than one type of skin on their face.
In fact this isn't unusual, because most people have more than one type at any given time, and types do change over the course of a lifetime. What makes combination skin stand out as a group of its own is simply that it's the most common kind of combination.
Combination skin is usually characterised by particularly oily patches of skin on the forehead, the nose, and the chin. This oily area forms the 'T' that gives T-Zone its name. The other areas of the face, such as the cheeks, the eyes and the area around the mouth are usually dry to normal.
T-Zone skin is caused by the glands beneath the surface of the forehead, nose, and chin over-producing a substance called sebum. Sebum is an oily substance who's job it is to keep the body's surface hydrated. When these glands produce too much Sebum, it builds up on the surface giving a slick, slippery look and feel.
Because of this over-production of Sebum, the pores on the forehead, nose and chin are often enlarged in people with this type, making them more prone to acne in these areas. Acne is a condition that occurs when pores become clogged with Sebum, which then interacts with bacteria, causing puss-filled lesions commonly called pimples, or spots. People with this type of skin tend to see the most frequent occurrences of acne in this 'T' area over their teenage years.
It's important for people with this type or grouping to understand that the two different types of flesh on their faces require different types of treatment. The better you understand the characteristics of your particular type, the better you're able to look after it!