mackenzie is a petite five feet tall. her bra size 32-h. uh-huh, h. somaking a drastic decision to go under the knife to surgically shrink the size of her breasts on her 18th birthday. >> someone told me i was going against god. he gave me a gift and i shouldn't be doing this. to them, i want to say, i don't care about your opinion because at the end of the day it's my body. >> reporter: it turns out mackenzie is far from alone. in the u.s. breast reduction surgeries have spiked 157%. why this uptick? some studies suggest girls today reach puberty earlier, pointing to the obesity epidemic or hormones in the modern diet. other experts say it is because the surgery has gotten so safe and artful. doctors tell us younger and younger women are seeking out the procedure raising questions are teenagers like mackenzie old enough to understand the risks? nipple sensitivity, and even losing the ability to breast-feed. >> i'm ready to take the chance because it will be worth with it in the end. >> the size of her breasts have taken a physical and emotional toll on