Body odours as a chemosignal in the mother-child relationship: new insights based on an human leucocyte antigen-genotyped family cohort

Abstract

Mothers are able to identify the body odour (BO) of their own child and prefer this smell above other BOs. It has hence been assumed that the infantile BO functions as a chemosignal promoting targeted parental care. We tested this hypothesis and examined whether children's BOs signal genetic similarity and developmental status to mothers. In addition, we assessed whether BOs facilitate inbreeding avoidance (Westermarck effect). In a cross-sectional design, N = 164 mothers participated with their biological children (N = 226 children, aged 0-18 years) and evaluated BO probes of their own and four other, sex-matched children. Those varied in age and in genetic similarity, which was assessed by human leucocyte antigen profiling. The study showed not only that mothers identified and preferred their own child's BO, but also that genetic similarity and developmental status are transcribed in BOs. Accordingly, maternal preference of their own child's odour changes throughout development. Our data partly supported the Westermarck effect: mothers' preference of pubertal boys' BOs was negatively related to testosterone for the own son, but not for unfamiliar children. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Keywords: body odour; chemosensory communication; hormones; major histocompatibility complex; olfaction; parent–child relationship.

Figure 1.

Study design and procedure. Session 1, sampling procedure; session 2, experiment with rating procedure.

Figure 2.

(a) Identification of BO probes depicted in % (i) across all children and (ii) for each age group. (b) Maternal preference of each BO probe and comparison between own child's BO versus all other samples depicted (i) across all children and (ii) for each age group. *p < 0.05; **p < 0.01, ***p < 0.001; n.s. = not significant (p > 0.05). Pleasantness is measured visual analogue scale, ranging from 0 (not pleasant at all) to 100(very pleasant).

Figure 3.

Maternal preference of BO probes depicted by identification behaviour: (a) left side: non-chosen BOs, right side: chosen BOs; (b) left side: non-chosen BOs depicted by age group; right side: chosen BOs depicted by each age group. *p < 0.05; **p < 0.01, ***p < 0.001. Pleasantness is measured visual analogue scale, ranging from 0 (not pleasant at all) to 100(very pleasant).

Figure 4.

Scatterplots for maternal pleasantness ratings of BOs in relation to hormonal levels depicted by age group and sex of the child. Blue dots, own child; grey dots, unfamiliar child. Pleasantness is measured visual analogue scale, ranging from 0 (not pleasant at all) to 100(very pleasant).