Depilatory laser miniaturizes hair by inducing bystander dermal papilla cell necrosis through thermal diffusion

Hsien-Yi Chiu; Wei-Hung Wang; Chen-Hsiang Kuan; Yueh-Feng Wu; Chung-Jen Tseng; Wen-Yen Huang; Shiou-Han Wang; Sung-Jan Lin

doi:10.1002/lsm.23533

Depilatory laser miniaturizes hair by inducing bystander dermal papilla cell necrosis through thermal diffusion

Lasers Surg Med. 2022 Aug;54(6):916-927. doi: 10.1002/lsm.23533. Epub 2022 Mar 15.

Authors

Hsien-Yi Chiu^{1

2

3

4}, Wei-Hung Wang¹, Chen-Hsiang Kuan^{5

6

7}, Yueh-Feng Wu¹, Chung-Jen Tseng³, Wen-Yen Huang¹, Shiou-Han Wang³, Sung-Jan Lin^{1

3

4

7

8}

Affiliations

¹ Department of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei, Taiwan.
² Department of Dermatology, National Taiwan University Hospital Hsin-Chu Branch, Hsinchu, Taiwan.
³ Department of Dermatology, National Taiwan University Hospital, Taipei, Taiwan.
⁴ Department of Dermatology, College of Medicine, National Taiwan University, Taipei, Taiwan.
⁵ Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
⁶ Division of Plastic Surgery, Department of Surgery, National Taiwan University Hospital and College of Medicine, Taipei, Taiwan.
⁷ Research Center for Developmental Biology and Regenerative Medicine, National Taiwan University, Taipei, Taiwan.
⁸ Brain Research Center, National Tsing Hua University, Hsinchu, Taiwan.

PMID: 35289409
DOI: 10.1002/lsm.23533

Abstract

Objectives: Depilatory laser targeting melanin has been widely applied for the treatment of hypertrichosis. Both selective photothermolysis and thermal diffusion have been proposed for its effect, but the exact mechanism of permanent hair reduction remains unclear. In this study, we explore the role of thermal diffusion in depilatory laser-induced permanent hair loss and determine whether nonpigmented cells are injured by thermal diffusion.

Materials and methods: C57BL/6 mice in anagen and telogen were treated with alexandrite laser (wavelength 755 nm, pulse duration 3 milliseconds, fluence 12 J/cm² , spot size 12 mm), respectively. Histological analysis, terminal deoxynucleotidyl transferase dUTP nick-end labeling assay, and transmission electron microscopic imaging were employed to evaluate the injury to hair follicle (HF) cells. The proliferation status of HF cells was examined by 5-bromo-2'-deoxyuridine pulse labeling. The number of HF stem cells was quantified by fluorescence-activated cell sorting. The size of the regenerated hair was determined by measuring its length and width.

Results: We found that irradiating C57BL/6 mice in anagen with alexandrite laser led to hair miniaturization in the next anagen. In addition to thermal disruption of melanin-containing cells in the precortex region, we also detected necrosis of the adjacent nonpigmented dermal papilla cells due to thermal diffusion. Dermal papilla cells decreased by 24% after laser injury, while the number of bulge stem cells remained unchanged. When the laser was delivered to telogen HFs where no melanin was present adjacent to the dermal papilla, thermal necrosis and cell reduction were not detected in the dermal papilla and no hair miniaturization was observed.

Conclusion: Our results suggest that depilatory laser miniaturizes hair by inducing thermal necrosis of dermal papilla cells due to secondary thermal diffusion from melanin-containing precortex cells in the anagen hair bulbs.

Keywords: depilatory laser; dermal papilla; hair follicle stem cell; necrosis; selective photothermolysis; thermal diffusion.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Hair Follicle
Hair*
Lasers
Mice
Mice, Inbred C57BL
Necrosis / etiology
Thermal Diffusion*