Humid-heat extremes threaten human health and are increasing in frequency with global warming, so elucidating factors affecting their rate of change is critical. We investigate the role of wet-bulb temperature (T-W) frequency distribution tail shape on the rate of increase in extreme T-W threshold exceedances under 2 degrees C global warming. Results indicate that non-Gaussian T-W distribution tails are common worldwide across extensive, spatially coherent regions. More rapid increases in the number of days exceeding the historical 95th percentile are projected in locations with shorter-than-Gaussian warm side tails. Asymmetry in the specific humidity distribution, one component of T-W, is more closely correlated with T-W tail shape than temperature, suggesting that humidity climatology strongly influences the rate of future changes in T-W extremes. Short non-Gaussian T-W warm tails have notable implications for dangerous humid-heat in regions where current-climate T-W extremes approach human safety limits. Plain Language Summary Extreme heat is more dangerous to humans when it is combined with high humidity, so it is important to understand how the combination of heat and humidity will change under continued global warming. We investigate how the current distribution of wet-bulb temperatures, a heat-humidity measure, influences how future wet-bulb temperature extremes will increase. Results show that locations with an asymmetrical wet-bulb temperature probability distribution, such that the warm side of the distribution is shorter than if the distribution were normally shaped, are likely to see a faster increase in extreme wet-bulb temperature days under the same warming compared with other locations. Results suggest that the underlying humidity climatology is a more important driver of this distribution asymmetry compared to the underlying temperature climatology.