Hydrogen mass fraction as a function of luminosity for the sample stars. Red triangles, blue circles, and grey squares refer to Galactic, LMC, and SMC stars, respectively. The horizontal dotted line marks the value X = 0.4. The figure also includes WNh stars from the literature: stars in R136 (Bestenlehner et al. 2020), star VFTS 682 (Bestenlehner et al. 2011), star B in NGC 3603 (Crowther et al. 2010), and stars in the Arches cluster (Martins et al. 2008). Literature objects in the LMC (Galaxy) are shown in cyan (pink) and by open symbols.