Phexxi comes in an applicator that women insert before sex. The gel made by San Diego-based Evofem Biosciences contains lactic acid, citric acid and potassium bitartrate, all of which are common food additives.

The new gel has some similarities to spermicides, which block the entrance to the cervix and slow sperm down. But Phexxi works differently.

The vagina's pH — a measure of acidity — is typically in the range of 3.5 to 4.5, the level needed to maintain healthy bacteria. Sperm raise that to a more hospitable level of 7 to 8. Phexxi keeps it in the usual acidic range, killing the sperm.

Unlike some other contraceptives, it only needs to be used shortly before sex and it doesn't contain hormones, which can cause side effects some women can't tolerate.

The company said Phexxi — pronounced FECK'-see — will have a list price of $250 to $275 for a box of 12 without insurance.

In a study of 1,400 women aged 18 to 35, Phexxi was about 86% effective on average over seven menstrual cycles and a total of more than 34,000 acts of intercourse. That's a bit better than condoms, spermicides and other "on-demand" contraceptives, but less effective than long-term methods such as IUDs and implants.