All Muslim women are supposed to do so. It is not particular for Shiite.
It is worth noting that the wearing of the niqab (which covers the front of the face) is actually more common among Sunni women than Shiite women, if only because of the laws and culture of Iran as compared to Sunni-majority Arabian countries.
Almost no Muslim men cover their faces. (If they do, it is for non-religious reasons such as putting on a mask to hide one's identity, etc.) Most Muslim women do show their face, either by wearing no headscarf or by wearing a hijaab or abaya/chador which leaves the entire face exposed. As concerns Muslim women who cover their faces in public, they will relax the covering in front of a group of all women or in front of men who are their close relations and thus unsuitable for marriage. I, as a non-Muslim, have seen Muslim faces.
There are a few ways one can try to cover up exposed acne. One can use foundation makeup and blusher to cover up acne. One can also buy specialist kits to help cover it from 'Exposed Skincare'.
Not all Muslim women cover their faces, but most of them cover only their hair. Of course, if you want to be a Muslim, you have to follow the teaching of Islam, the Islam asks women to at least cover their hair.
The temperature of a region with cloud cover is lower than a region without cloud cover. This is due to the absorption of heat of the clouds and the reflection of the water molecules in the clouds of light that causes the heat in the region.
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Women having to cover their hair.
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