Serum are like magical drops that give nourishment to your skin. This is a dermatologically tested product, which means that it's been tested on humans.
From Amazon
Burts Bees Complete Nourishment Facial Oil for Women 0.51 oz Oil 15 ml (Pack of 1),White
Vitacost
Burt's Bees Complete Nourishment Facial Oil - Anti-Aging Oil 0.51 fl oz