How does an excessive amount of beta carotene affect skin colour?
How much beta carotene does it take to change someones skin colour?

To turn the skin yellow, rather than orangish, a person would have to eat about 10 carrots a day for a period of at least two weeks, consuming at least 51 grams of beta-carotene each day. The average carrot contains about 5 to 6 milligrams of beta-carotene



What is the reason behind this?

A very high diet of food which contain carotenemia (such as carrots, squash, sweet potatoes and others) can cause skin discoloration. The skin, and especially the palms of the hands, turn yellow, rather than orange. This change in skin colour fades and eventually disappears when the individual's diet changes back to normal.


  Carotenoderma is deliberately caused by beta-carotenoid treatment of certain photosensitive dermatitis diseases such as erythropoietic protoporphyria, where beta carotene is prescribed in quantities which discolor the skin.




What does an excess of carotenoids do? 


  An excess of carotenoids, being eliminated via sweat, may cause a marked orange discoloration of the outermost skin layer. This benign and reversible condition – which is most easily observed in light-skinned people and may be mistaken for jaundice – is known as carotenosis or carotenoderma. 




sources: 


https://en.wikipedia.org/wiki/Carotenosis 
http://www.webmd.com/vitamins-supplements/ingredientmono-999-beta-carotene.aspx?activeingredientid=999&amp; 
http://umm.edu/health/medical/altmed/supplement/betacarotene 
http://emedicine.medscape.com/article/1104368-overview