Why might a teenager feel self-conscious about his or her blemishes or other skin problems?

Answer:because of other peoples opinions

They're worried about perception and the only teens they've seen in movies have perfect skin, so they feel different.

Explanation:

Generally in media, teens are played by young adults whose adolescent acne has already left them. Also, skin problems are generally perceived as a reflection of one's inner health, which isn't always true. So in short, they're just scared of what others will think of them.