Wild spurges make risky houseplants.

Euphorbiaceae is one of botany's bigger families. Its 8,000 or so distinct species--known generically as spurges--produce a milky latex sap that oozes from cuts on leaves or stems. The fact that this latex usually contains allergy-inducing toxins hasn't stopped aficionados from cultivating scores of spurges as ornamental houseplants. Among the most popular are poinsettias, crotons, and crown-of-thorns.

Now, German biochemists offer more reason to handle spurges with care. Their latex, which easily penetrates skin, can contain ingenol--a potent tumor-promoting chemical. If someone who has been exposed to carcinogens, such as a smoker, touches this latex, "it might accelerate a tumor's development," worries Heinrich Sandermann Jr. of the GSF-National Research Center for Environment and Health in Oberschleissheim.

To gauge the risk faced by people who work with spurges, his team screened 22 houseplant cultivars using animal cells engineered to emulate precancerous cells and also to glow when they undergo a cancer-like transformation.

Twenty cultivars, including eight crotons and seven poinsettias, exhibited virtually no cancer-promoting activity, the scientists report in the September ENVIRONMENTAL HEALTH PERSPECTIVES. Two relatively wild spurges, however, triggered plenty of glow. The good news, Sandermann says, is that the most common spurges "appear to pose little risk."