Across many different taxa, individuals assess potential mating partners via telereceptive senses such as vision, olfaction, and hearing (Aglioti & Pazzaglia, 2011). Although some vertebrates appear to rely predominantly on a single sense (Arakawa, Blanchard, Arakawa, Dunlap, & Blanchard, 2008; Candolin, 2003; Gosling & Roberts, 2001), most species, including humans, employ multiple senses (Candolin, 2003; Higham & Hebets, 2013) in their assessment. Frog calls, for example, are often accompanied by conspicuous vocal sac movements and/or water surface vibrations, while many bird species show complex, rhythmic and vigorous visual displays during courtship singing (for a review, see Halfwerk et al., 2019).

Perceived variation in these physical traits may provide information about an individual's mating-related quality, such as health and fertility (e.g., Grammer, Fink, Møller, & Thornhill, 2003; Rhodes, 2006; Thornhill & Gangestad, 1999b). As the judgment of an individual's attractiveness based on any single modality entails a certain level of error, using multiple sensory channels could enable a more reliable assessment (Møller & Pomiankowski, 1993). Two competing hypotheses have been proposed to explain the use of multiple modalities in the assessment of potential mates (Groyecka et al., 2017; Higham & Hebets, 2013). According to the ‘backup signals’ hypothesis (Grammer, Fink, Juette, Ronzal, & Thornhill, 2001; also coined redundant signalling, Møller & Pomiankowski, 1993; Thornhill & Grammer, 1999), certain cues may provide similar (redundant) information; assessing this same information in several different modalities will then tend to reduce error and facilitate a more accurate overall assessment of underlying quality. In contrast, the multiple messages hypothesis (Cunningham, Barbee, & Pike, 1990; Møller & Pomiankowski, 1993) suggests that each trait provides distinct and independent (non-redundant) information about an individual's mating-related quality, but in combination, these can facilitate more accurate assessment of overall individual quality than any single cue in isolation. With all this in mind, we can make predictions to test these two ideas. One can expect that if attractiveness assessments based on different sensory channels are closely and positively associated, such congruence would suggest redundancy in information across traits and provide support for the backup hypothesis. Weak or absent cross-modal congruence (i.e. cues convey non-redundant information), however, would support the multiple messages hypothesis. The mating-related animal research provided some support for both of these hypotheses. The use of backup signals of quality was demonstrated, for instance, in Drosophila saltans where removing one courtship component (either visual, auditory, chemical or tactile) did not eliminate the female's decision to mate (Colyott, Odu, & Gleason, 2016). On the other hand, the study on peacock spiders (Maratus volans) showed that both visual and vibratory signalling is important for mating success supporting the multiple messages hypothesis (Girard, Elias, & Kasumovic, 2015). Overall, the majority of available animal research seems to provide more evidence in favour of the multiple messages hypothesis (Candolin, 2003).

Most research on human mate preferences has focused on visual cues, typically by investigating people's assessments of facial and/or body attractiveness. Although physical appearance certainly plays a prominent role (Groyecka et al., 2017; Herz & Inzlicht, 2002; Walter et al., 2020), the assessment of attractiveness in potential mating partners is undeniably multimodal. Research suggests that body odour (Havlíček et al., 2008; Roberts et al., 2011) and vocal cues (Hill & Puts, 2016; Pisanski, Feinberg, Oleszkiewicz, & Sorokowska, 2017; Zäske, Skuk, & Schweinberger, 2020) also contribute substantially to human mate preferences (Groyecka et al., 2017). However, studies that examine potential cross-modal congruency and redundancy of attractiveness judgments are scarce. In one of the first such studies, Rikowski and Grammer (1999) reported a positive relationship between judgments of women's faces and their body odour. They also found a similar association in men's faces and odour, when rated by women in the fertile phase of their menstrual cycle Note that authors assessed cycle phase based on counting methods which appears to be highly unreliable, see Gangestad et al., 2016; Havlíček & Roberts, 2022). Rikowski and Grammer concluded that human faces and body odours provide similar information about mate quality. Several other studies have subsequently reported positive associations between perceived attractiveness of faces and body odours (Mahmut & Stevenson, 2019; Roth, Samara, & Kret, 2021; Thornhill et al., 2003; Thornhill & Gangestad, 1999a), although the strengths of some associations were weak and two other studies (Roberts et al., 2011; Röder, Fink, & Jones, 2013) found no support for this association (see Table S0–6 and Fig. 2). Collectively, the available studies provide some support for both the backup signals and multiple messages hypotheses.

In view of this, we set out to conduct a systematic review and meta-analysis of the relationship between human body odour and facial attractiveness, to test between the two hypotheses. We collated the published studies and complemented these with unpublished datasets. During this process, we noticed that several of the unpublished datasets that we obtained from researchers also contained ratings of perceived vocal attractiveness. Therefore, we also performed meta-analyses of congruence between body odour and vocal attractiveness. As body odour perception and its relation to other modalities are still somewhat overlooked research topics, we focus our study primarily on the relationships between body odour attractiveness and other sensory modalities. Although of interest, the investigation of the association between facial and vocal attractiveness to a comparable extent (e.g. collecting both published and unpublished evidence) is beyond the scope of the current study.