Here's a post from Huffington Post that addresses this issue. I'm not sure I agree with it all but it is something that is rarely covered... Excuse me while I go tweeze my eyebrows...
http://www.huffingtonpost.com/2015/...ing_n_3749690.html?ncid=fcbklnkushpmg00000063
http://www.huffingtonpost.com/2015/...ing_n_3749690.html?ncid=fcbklnkushpmg00000063