Spermicides are substances that are sperm killing.

Usually they are used to increase the effectivity of contraceptive barrier methods like diaphragms and condoms, they are only somewhat effective alone.

The most common active ingredient of spermicides is nonoxynol-9, to which some people are allergic. Nonoxynol-9 has been shown to increase the risk of contracting HIV because it creates tiny abrasions in the vaginal and anal walls that make contraction of HIV and other STIs more likely.

See also Sperm