Development of a New Grading Scale for Evaluating Overall Hair Density

Background Hair density influences overall attractiveness significantly. Although pre‐existing classifications have been used to describe alopecia pattern and evaluate treatment efficacy, their accuracy is undesirable. Objective The aim of this study is to develop a stepwise and accurate graded visual scale regardless of sex and verify its application value in response to treatment efficacy. Methods Based on 6644 standard images, the seven‐point grading scale for overall hair density was developed to describe alopecia extent. Reliability and validity studies were conducted to identify intra‐rater and inter‐rater consistency. Image J and Dermoscopy were introduced to quantify macro‐ and micro‐hair characteristics and determine the gradient difference of the classification system. The sensitivity to treatment response was verified by one model trial to evaluate its application value. Results The intra‐rater and inter‐rater reliability revealed excellent agreement and consistency of the severity grading, independent of the time of evaluation and evaluator. Moreover, quantitative hair characteristics, including global exposed scalp area ratio, hair diameter, local hair density, vellus hairs ratio and vellus to terminal hairs ratio, were closely related to the corresponding grades. In the model trial, overall hair density evaluated by this scale has significantly improved in the test group, while there was no obvious change in the control group. The observed trend of the evaluation result was consistent with changes in the global exposed scalp area ratio and local hair density. Conclusions The new grading scale represents a reliable and objective indicator for a valid, reproducible, and sensitive evaluation of alopecia extent and treatment response.