Face masks cover the sun and black teeth

I noticed that a lot of Vietnamese women wear face masks similar to the women in China, so I assumed it was for the same reason - protection against pollution. But for Vietnamese women, it's a lot more than that. Yes, they want protection from pollution but they also want to cover themselves so they don't get tanned. As you can see, their masks don't just cover the mouth, but rather cover everything but their eyes. And similar to most Asian cultures, pale skin is considered more beautiful than tanned skin.
Lastly, in the past, women used to chew betel nuts (Bing Lang). I'm not familiar but its suppose to have a black licorice flavor and give you a caffeine high. At the same time, it turns your teeth black. It used to be considered beautiful for women to have dark teeth. Now, because white teeth is considered beautiful worldwide, Vietnamese women who used to chew betel nuts cover their less-attractive darkened teeth with face masks.
Just as a side note, have you heard of the Betel Nut Girls in Taiwan? These are scantily-clad women who sell betel nuts on sidewalks, targeting mostly male drivers. Now the Taiwanese government is trying to crack down on these women, believing they wear too little clothing. Check out this article and decide for yourself: http://www.stewpig.com/sexy/taiwan-betel-nuts-bing-lang-girls-26-photos/2009/10/09/.