>While self-selection is unlikely to explain the GAP, another potential artifact of data collection could be systematic differences in grooming practices between genders. Women typically invest more time and resources in grooming than men (Das & Stephen, 2011). However, most studies follow standardized photo-shooting protocols requiring participants to remove makeup and other enhancing accessories (e.g. Ebner et al., 2018; Kleisner et al., 2024; Torrance et al., 2014; Zhang et al., 2019). While some grooming practices, such as eyebrow shaping or long-term skincare routines, may not be entirely controlled by these protocols, their impact is likely minimal.

I disagree with their premise that this impact is "likely minimal". I also would want to know what percentage "most studies" refers to.