A predicted interaction between odour pleasantness and intensity provides evidence for major histocompatibility complex social signalling in women.

Major histocompatibility complex (MHC) social signalling has been found in over 20 vertebrate species so far and is ‘likely the basis for a vertebrate-wide chemosensory communication system’ [1]. Numerous further examples of MHC social signalling have been published since Ruff et al.’s [1] exhaustive review, both demonstrating female reactions to MHC sharing with males (e.g. [2,3]) and male reactions to MHC sharing with females (e.g. [4–7]). When concentrating on experimental studies in humans, 15 papers so far claimed to provide evidence for MHC-linked odours and/or odour preferences (electronic supplementary material, table S1), and a recent meta-analysis concluded thatMHC-linked preferences are ‘likely conserved across primates’ [8]. Well-worked-out cases of absent MHC social signalling would therefore be interesting exceptions of what seems to be a general rule, and it is important to find and document such exceptions to learn more about the principles of social signalling. However, easy as it is to miss an existing effect (e.g. because of problematic experimental protocols or low statistical power), it is just as challenging to demonstrate that an effect does not exist. Probst et al. [9] argue that ..