Carrageenan, an extract from red algae, was identified over a decade ago as a potent inhibitor of human papillomavirus (HPV) infection in vitro. Following this discovery, several studies evaluated carrageenan's anti-HPV activity in cells, experimental animals, and humans. We reviewed the evidence for carrageenan's anti-HPV activity. Studies had to be in vitro, in vivo, or in humans and report on carrageenan's anti-HPV activity. Of the 39 records identified in PubMed and 29 records in Clinicaltrials.gov, 22 records were included after screening: eight in vitro (including two ex vivo), three in vivo, five in vitro and in vivo, three clinical studies, and three trial protocols. A total of 12 studies evaluated carrageenan exclusively, while seven considered carrageenan combined with additional anti-viral or other agents. One study protocol will evaluate carrageenan exclusively and two others will evaluate carrageenan-combination products. Most clinical studies evaluated carrageenan's ability to prevent HPV acquisition (n=4), while one study explored its ability to promote clearance of existing infection (defined as absence of HPV DNA detection). Carrageenan's anti-HPV activity was observed consistently across study designs, except in two studies: one in vitro study where two of the HPV types tested were not significantly inhibited by carrageenan and one phase IIB trial in gay, bisexual, and other men who have sex with men. This review supports the premise that carrageenan, alone or in combination with other anti-viral agents, might be a potential prevention strategy complementary to HPV vaccination for women.
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