All it takes is frequent skin-to-skin contact with an arm, shoulder or leg that’s been slathered with a product containing estrogen, progesterone or testosterone.
The symptoms of secondary exposure can be alarming. Young children of either gender may develop enlarged genitals and start sprouting pubic hair and breasts. Dogs and cats that lick estrogen cream off an owner’s skin may act as if they are in heat, even if they are spayed...
Dr. Metzger has seen cases such as a baby whose genitals were enlarged because a grandpa on testosterone cream wasn’t in the habit of washing his hands before changing the child’s diapers...
Topically-applied medications are thought to pose fewer risks for primary users than oral medications, so their use has markedly increased.
Link. Another article on this subject at the New York Times.
I never knew that it could actually happen though. Some episodes of House seem a little far fetched.
We laughed long when he read the list because it states very clearly, "Do not apply to your penis or testicles!" I can totally see some guy thinking that he could get more from the gel if only he was creative about where he applied it.