Spermicidal vaginal jellies, creams, gels, suppositories, and foams, in addition to their toxic effect on sperm, also act as a mechanical barrier to entry of sperm into the cervical canal. The majority of spermicides marketed in the U.S. contain nonoxynol 9, which is a long-chain surfactant that is toxic to spermatozoa. Spermicides may be used alone or in conjunction with a diaphragm or condom. Some of the foam tablets and suppositories require a few minutes for adequate dispersion throughout the vagina, and failures may result if dispersion is not allowed to occur. In general, when used alone, spermicides have a failure rate of about 15% per year. Rarely, these chemical agents may irritate the vaginal mucosa and external genitalia. Recent evidence indicates that spermicides containing nonoxynol-9 (N-9) are not effective in preventing cervical gonorrhea, chlamydia or HIV infection. In addition, frequent use of spermicides containing N-9 has been associated with genital lesions which may be associated with an increased risk of HIV transmission.