Hygiene and attractiveness consequences of Speedos versus swimming shorts: results of a cross-over study among male academics

Whilst in most northern European countries swimming shorts are the norm, swimming briefs, or Speedos, are compulsory in France and parts of Italy. Hygiene is the main justification for this measure, but empirical data is lacking and consequences for psychological well-being remain unaddressed. This study aimed to empirically assess the hitherto theoretical risk to public pool hygiene posed by swimming shorts, as compared to form fitting swimming briefs (Speedos) that are required swimwear in several southern European countries.

The study design was a cross-over study and photo elicitation, involving international adult male academics and technical staff, of varying age (20-54) and BMI (17.8-25.7). Speedos or swimming shorts were worn for two hours during the normal working day to assess bodily contamination, or as swimwear in natural water bodies to assess environmental contamination. The primary outcome was the number of colony-forming units (CFU) of Gram-positive bacteria (GPB) and Gram-negative bacteria (GNB) on agar plated with 100 µL water collected from i) submersion of the swimming garments in clean tap-water (bodily contamination), or ii) residual water from natural sources (environmental contamination). The main secondary outcomes were self-perceived and externally assessed attractiveness of anonymized photos of study participants wearing both swimwear types.

GPB and GNB growth was significantly higher after incubation with tap water rinsed from submersed shorts compared to Speedos (rank-sum, GPB p<0.0400, GNB p=0.0100). Swimming in natural water resulted in considerably higher levels of GNB on Speedos (median 600 CFU/litre, interquartile-range (IQR): 600 to 31400) and shorts (median 33800, IQR: 5200 to 91000), but sample sizes were too low for formal analysis. Participants were significantly less attractive to external judges in Speedos compared to shorts (p<0.0067), but not when judged by themselves (Wilcoxon paired sign rank test: p=0.3394).

We conclude that both GPB and GNB contamination were more abundant in water exposed to swimming shorts, as compared to Speedos. Externally assessed attractiveness was lower in Speedos.