Why do kpop idols wear masks?

Big Bang's G-Dragon
As you can see from the picture above, many k-pop idol stars wear masks when they go out, especially when they arrive at the airport. Do you know why?

Apink's Jung Eunji
"At first, k-pop idols began to wear masks to shield their faces. Most of them have very small face, and masks are really good items to hide their faces. That’s why they wear masks when they did not wear makeups or are not ready to be photographed. For instance, they could have skin problems after a long-distance flight, but it's quite cumbersome to wear full makeup. And if they date somebody in public, yes, masks are essential. K-pop idols are high quality goods produced by their agencies, and wearing masks is a kind of way to maintain their merchantable qualities."

B1A4's Shinwoo
"By the way, k-pop idols' purpose of wearing masks has been changing. When you see handsome idol stars wearing masks, how do you feel? Yeah, they look awesome. Mask is now regarded as a kind of the latest fashion among kpop idols. Do you think all the idols wear masks because they didn’t wear makeups or want to hide their faces? No, they wear full makeups before they wear masks. And you know, even less famous idols wear masks too in public even though nobody knows who they are."

Infinite's Woohyun