Spermicides kill sperm, stopping them from swimming to an egg and starting a pregnancy, which kills sperm. Spermicides come in suppositories, foams, creams, inserts, film and gels (but all have the chemical nonoxynol-9). You can use a spermicide alone, but it's more effective at preventing pregnancy when used with a condom or diaphragm.

Spermicides are inserted into the vagina before intercourse. With some products, like film, inserts and suppositories, you have to wait a little while - usually 15 to 30 minutes - before having intercourse, so the warmth of your body can melt the spermicide. Foams, creams, and gels,however, are effective as soon as they are inserted.

When used alone and perfectly (every time you have sex), spermicides prevent pregnancy about 82 percent of the time. With more typical use - mistakes and all - spermicides prevent pregnancy about 70 to 75 percent of the time. Add a condom and you've just improved the chance of preventing pregnancy and infection. Together they can prevent pregnancy 97 percent of the time - a much safer rate.

Some women can be allergic to the chemicals used in spermicides. Soreness, itching, redness, and swelling are the most common allergy symptoms. If a woman has a reaction to the spermicides and has unprotected sex with her partner, then the rubbing against the irritated skin can make her more open to contracting an STD if her partner has one. So, spermicides should be used with a condom to prevent pregnancy and infection.

Spermicides are sold in many drug stores and pharmacies, as well as online and in family planning clinics. One tube of gel or cream typically costs about $8 to $10. One dose of an insert, film or foam typically costs about $1 and is sold in packs of 3, 6, or more.

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