Hair loss, complex due to individual and ethnic variations, remains difficult to visually quantify. Previous research suggests hair loss becomes noticeable to patients only after a 50% reduction in total scalp hair; however, no study has defined the minimal change in hair counts which result in noticeable hair loss. Our study sought to identify when hair loss becomes noticeable to professionals, thereby informing treatment initiation and adjustment and setting realistic patient expectations.

In our NYU School of Medicine institutional review board–approved study, we aimed to identify the minimum discernable hair loss difference recognized by dermatologists. Using the Canfield HairMetrix device, we obtained standardized pretreatment and posttreatment global scalp photographs and hair counts of 100 patients with androgenetic alopecia, stratified into 7 density groups per Sturges’ rule, and developed a survey featuring 2 photos from each density group (Supplementary Fig 1, available via Mendeley at https://doi.org/10.17632/6kchv6h4dh.2). A sample size of 120 dermatologists was selected based on feasibility and the need for diverse perspectives. Of the participating 120 board-certified dermatologists, 100 responded (83.33% response rate), via email (85/105) and in-person (15/15).