While the latest trend is apparently rubbing your muscles with Preparation H to achieve a ripply Schwarzenegger effect, one topical substance that might be far more useful for men is estrogen. Researchers at the University of Melbourne are saying that men could considerably reduce their risk of contracting HIV by applying estrogen cream to their penises at least once a week. The reason it works, according to U. Melbourne professor Roger Short, is that the estrogen can dramatically thicken the layer of keratin, the protein that's a key ingredient in hair and nails, covering the skin of the penis. Because of its toughness and insolubility, the keratin layer would presumably provide a natural defense against the virus. Calling the cream a "natural condom," Short told the Australian Broadcasting Corporation that he believed the cream would create "a biological membrane which the virus can't get through." Of course, he and his team have yet to test this keratin theory in actual trials, and there's always the small matter of a cream doing nothing to prevent pregnancy or other sexually transmitted infections. Still, given that mere calls for abstinence and condom distribution have done little to halt the spread of AIDS, perhaps a quick weekly dousing with estrogen could go a long way.