Ultraviolet light from the sun changes a substance in the skin into vitamin D.

VOA: special.2009.04.21

so much understanding of how skin responds to light, how hair moves,

对皮肤对光的反应、头发的摇动，有很多的理解，

没有特效的话 - SpeakingMax英语口语达人

Light and heat from the sun can change chemicals in the skin.

VOA: special.2010.07.06

People with light-colored skin, hair or eyes are at greatest risk.

VOA: special.2010.07.06