What makes our skin oily or dry?

Why do we have oily or dry skin? A dermatologist explains the root cause and how it can change over time.

"We see dry skin, we see oily skin, there can be skin that's in between. And we can also see skin that's sort of a combination," Dr. David Pearson said. "And when we think about combination skin, it's oily in one area, often in that T-zone, the forehead and down the central part of the face, and dry on the periphery."

Pearson is a dermatologist who teaches at the University of Minnesota Medical School.

"Usually, the two big categories are oily skin vs. dry skin," he said. "They are different, you know. Oily skin, usually what we are talking about is how much sebum is on the skin. So sebum is the main oil that we think about. And sebum comes from sebaceous glands."

Sebum is an oily