Genetic differences determine whether a component of male body odor smells like sweat, something sweet, or nothing at all, according to newly published research. The component is the steroid androstenone (shown), a testosterone derivative that is present in sweat. To some people, androstenone smells pleasant, with a sweet, floral, or vanilla-like scent. Others find the compound's "sweaty" odor offensive and liken it to urine. A third group can't even smell the compound. The variability in people's perception of androstenone is due in large part to genetic variations that affect the odorant receptor OR7D4, report Leslie B. Vosshall of Rockefeller University, Hiroaki Matsunami of Duke University, and colleagues (Nature, DOI: 10.1038/nature06162). The researchers determined that people who find androstenone unpleasant have two single-nucleotide polymorphisms in the gene for the receptor that is expressed in sensory cells in the nose. In vitro studies showed that these mutations severely impair the receptor's function. Matsunami says the work represents the first demonstration of a link between the performance of a human odorant receptor and how that odor is perceived.