An assortment of hand cleaners that flooded into the market after mainstays disappeared from retail outlets contain high levels of benzene, according to Valisure, a New Haven, Connecticut-based online pharmacy that tests products for quality and consistency.

Benzene causes cancer, according to the U.S. Department of Health and Human Services. The World Health Organization’s cancer research arm puts it in the highest risk category, on par with asbestos.

Valisure analyzed 260 bottles from 168 brands and found 17% of the samples contained detectable levels of benzene. Twenty-one bottles, or 8%, contained benzene above two parts per million, a temporary limit the FDA set for liquid hand sanitizers to ease the supply squeeze.