Two new molecules kill sperm 25 times more effectively than the most commonly used spermicide, without irritating vaginal cells.

Nonoxynol-9 (N9) is the active ingredient in most spermicidal creams and is sometimes used to lubricate condoms. It is a detergent that kills almost all living cells by destroying their fatty membranes – in the same way that household detergent breaks up grease.

While this kills sperm, it also wipes out some of the normal vaginal bacteria that help prevent bladder and yeast infections. N9 can also irritate cells in the cervix and vaginal wall in some women, leaving them more susceptible …