Ingredient might prevent sexually transmitted disease.

A seaweed derivative that's commonly added to baby food, lubricants, and other consumer products as a thickening agent can inhibit the virus that causes cervical cancer and genital warts.

About 20 million Americans are infected with the human papillomavirus (HPV). Although people can reduce their chances of acquiring HPV by using condoms (SN: 6/24/06, p. 387) or receiving a new vaccine (SN: 10/15/05, p. 243), scientists have long sought a chemical that could be a topical HPV microbicide.

While studying chemicals that affect HPV's penetration of cells, Christopher Buck and his colleagues at the National Cancer Institute in Bethesda, Md., realized that the seaweed derivative carrageenan has a molecular structure that might block the virus.

Sure enough, when the researchers mixed carrageenan and HPV with human cells in a test tube, individual viruses couldn't get inside the cells. No other microbicides known to inhibit HPV infection worked as well at carrageenan's effective dose, says study co-author John Schiller, also of the National Cancer Institute.

Since carrageenan is a common ingredient in a variety of consumer products, including some sex lubricants, the researchers tried the same test with lubricants containing carrageenan and those without it. Only the carrageenan-containing lubricants inhibited HPV particles from entering cells, the researchers report in the July PLoS Pathogens.

Though carrageenan-containing products prevent HPV infection in the lab, Schiller notes that it's too early to say whether they do so in people. "Until we do clinical trials, we don't want people modifying their behavior based on false ideas of how carrageenan can protect them," he says.--C.B.