In his original study Dr Wedekind recruited female volunteers to sniff men's three-day-old T-shirts and rate them for attractiveness. He then analysed the men's and women's DNA, looking in particular at the genes that build a part of the immune system known as the major histocompatability complex (MHC). Dr Wedekind knew, from studies on mice, that besides fending off infection, the MHC has a role in sexual attractiveness. It changes odours in ways the mice can detect (with mice, the odours are in the urine), and that detection is translated into preferences for particular mates. What is true for mice is often true for men, so he had a punt on the idea that the MHC might affect the smell of human sweat, as well.
It did. Women preferred T-shirts from men whose MHC was most different from their own. What was more, women with similar MHCs favoured the use of similar commercial perfumes. This suggests that the role of such perfumes may be to flag up the underlying body scent rather than mask it, as a more traditional view of the aesthetics of body odour might suggest.