Paradoxical hypertrichosis (PH) is an uncommon, poorly understood adverse effect associated with laser or intense pulsed light treatment for hair removal.
The objective of this study was to conduct a systematic review and meta-analysis to determine PH prevalence and associated risk factors.
We conducted a systematic review and meta-analysis of studies evaluating hair removal with lasers or intense pulsed light. Primary outcome was PH prevalence. Meta-regression and subgroup analysis were used to investigate associations among treatment modality, patients’ characteristics, and PH.
Included were 9733 patients in two randomized controlled trials and 20 cohort studies (three prospective and 17 retrospective). Pooled PH prevalence was 3% (95% confidence interval 1–6; I2 = 97%). Paradoxical hypertrichosis was associated with a face or neck anatomic location, and occurred in only 0.08% of non-facial/neck cases. Treatment modality and interval between treatments had no effect on the PH rate. There were insufficient data to determine the association between sex and skin type to PH. In three out of four studies, PH gradually improved with continued therapy.
Based primarily on cohort studies, PH occurs in 3% of patients undergoing hair removal with lasers or intense pulsed light, yet rarely outside the facial/neck areas. Treatment modality does not seem to be a contributing factor. Continuation of treatment in areas with PH may be the most appropriate treatment.
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We acknowledge the help of Dr. Debby Mir with English editing (Rabin Medical Center, Petah Tikva). She did not meet the criteria for authorship.
This publication was supported by Alma Lasers Ltd., Caesarea, Israel.
Conflict of interest
Igor Snast, Ran Kaftory, Moshe Lapidoth, and Assi Levi have no conflicts of interest that are directly relevant to the content of this article.
No ethics approval was needed because data were retrieved from previously published studies in which informed consent was obtained by the primary investigators.
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IS and AL were responsible for the data analysis and wrote the first draft of the manuscript. All coauthors contributed to writing of the manuscript. All co-authors provided important intellectual input and approved the final version of the manuscript.
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Snast, I., Kaftory, R., Lapidoth, M. et al. Paradoxical Hypertrichosis Associated with Laser and Light Therapy for Hair Removal: A Systematic Review and Meta-analysis. Am J Clin Dermatol 22, 615–624 (2021). https://doi.org/10.1007/s40257-021-00611-w