Supplementary Material for: Hair Care Habits and Frontal Fibrosing Alopecia: A Case-Control Study

Background: Frontal fibrosing alopecia (FFA) has been associated with hair cosmetic habits, yet causality and frequency-dependent effects remain uncertain.
Objective: To evaluate the association between hair care habits and FFA.
Methods: An analytical case–control study was conducted including 115 FFA patients and 112 matched controls, evaluated at the Hospital Italiano de Buenos Aires between 2015 and 2024. Participants reported current hair washing frequency, cosmetic hair practices, leave-in-product use, and sunscreen use; FFA cases also reported habits five years before symptom onset. Logistic regression models were performed.
Results:
Decreasing hair washing frequency was associated with progressively higher odds of FFA (adjusted OR 18.7 for washing ≤1 time/week compared with daily washing). In dichotomized models, daily washing remained protective (adjusted OR 0.31; p = 0.012). Cosmetic hair procedures ≥2/year and leave-in product use ≥1/week significantly increased risk (adjusted OR 2.39 and 4.98, respectively). sunscreen use showed no association with FFA in any model.
Discussion:
Frequent cosmetic procedures and leave-in product use were associated with higher odds of FFA, whereas daily washing was protective. These findings underscore the potential contribution of cumulative exposure to cosmetic substances in FFA pathogenesis and highlight modifiable behavioral factors warranting further study.