Picking a Side: Preferential Laterality in Scalp Hair Density.

Introduction: Clinical examinations of the scalp have shown that patients may grow hair preferentially at higher density on one side of their scalp, yet review of the literature to date has not yield studies that directly assess differences in scalp hair density laterality. The objective of this study was to examine whether scalp hair growth occurs preferentially and on which side of the scalp, the right or left, in healthy patients.

Method: Scalps of healthy subjects with no history of hair loss or scalp disease were imaged with digital trichoscopy at a university dermatology clinic. Bilateral temporal photos were uploaded to trichoscopy software for quantitative analysis.

Results: Scalp hair laterality was observed in both male and female, with no trend in left or right preference. While subjects who identified as Asian or Hispanic exhibited a strong laterality preference, statistical significance was not reached among African American or Caucasian subjects.

Conclusion: No overall side preference was observed in the study population, yet many of the healthy individuals tend to preferentially grow more hair on one side of their scalp. It is possible that in addition to genetics, certain behavioral or environmental factors may play a role in laterality.