Papillomavirus infections spike in sunny months.

Women tempted by a little hanky-panky at the beach this summer might give this some thought: Getting sun could increase their vulnerability to a sexually transmitted virus--and, ultimately, to cervical cancer.

Human papillomavirus (HPV), a common sexually transmitted infective agent, sometimes causes cervical cancer in women. Looking for seasonal patterns in infection rates, William Hrushesky of the W.J.B. Dorn Veterans Affairs Medical Center in Columbia, S.C., and his colleagues reviewed Dutch data on nearly 1 million Pap smears. The tests, each of which revealed whether a woman had been infected with HPV and whether she'd begun to develop cervical cancer, were conducted between 1983 and 1998 as part of a routine screening program in the Netherlands.

Pap smears positive for HPV infection were most frequent in August, Holland's sunniest month. Infections were about twice as common then as in the darkest months, Hrushesky says. Exposure to HPV through sexual activity, which in the Netherlands changes relatively little throughout the year, couldn't explain the seasonal infection pattern, he says. But sunlight's ultraviolet radiation could, because it's known to suppress the immune system and might make the lining of the cervix more susceptible to virus particles introduced during sex.

"The sun ... influences whether HPV takes hold; Hrushesky theorizes, adding that preliminary data also suggest that the sun plays a role in whether an HPV infection develops into cervical cancer. In fact, he says, "sunlight may be more important to cancer progression than to cancer initiation."--B.H.