Definition
Laser hair removal is a permanent hair elimination technique using photonic energy to destroy hair follicles through selective photothermolysis. This method relies on the preferential absorption of laser light by hair melanin, generating heat capable of destroying the follicular germ without damaging surrounding tissues.
Comparison of laser hair removal technologies
Comparative table of the main laser technologies used in hair removal
| technology | wavelength_nm | wavelength_µm | chromophore | penetration_depth_mm | optimal_phototypes | efficacy_12months | efficacy_3sessions | pulse_range_ms | fluence_range | advantages | limitations |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Ruby | 694 | 0.694 | Melanin | 0.4-1.0 | I-III | 70-90% | 45-60% | 20-300 | 40-60 J/cm² | Excellent melanin absorption | Burn risk on dark phototypes |
| Alexandrite | 755 | 0.755 | Melanin | 1.0-2.0 | I-IV | 75-85% | 55-65% | 3-20 | 10-18 J/cm² | Good penetration, speed | Variable memory effect |
| Diode 808 nm | 808 | 0.808 | Melanin | 1.5-3.0 | I-V | 70-80% | 57.9% | 5-100 | 10-40 J/cm² | Optimal penetration, versatility | Residual hemoglobin absorption |
| Diode 940 nm | 940 | 0.940 | Melanin | 2.0-4.0 | III-VI | 65-75% | 50-60% | 5-100 | 10-40 J/cm² | Better penetration, safety for dark phototypes | Lower melanin absorption |
| Nd:YAG | 1064 | 1.064 | Melanin | 3.0-6.0 | IV-VI | 60-70% | 45-55% | 10-300 | 100-200 J/cm² | Excellent tolerance for dark phototypes | Reduced melanin absorption |
| IPL | 500-1200 (broad spectrum) | 0.5-1.2 | Melanin, hemoglobin | 0.5-5.0 | I-IV | 50-70% | 40-50% | 2.5-25 | 15-35 J/cm² | Versatility, global treatment | Less specific than monochromatic lasers |
General mechanism of selective photothermolysis
Selective destruction of the hair follicle relies on three fundamental principles established by Anderson and Parrish
:
selection of a wavelength preferentially absorbed by hair melanin,
limiting pulse duration to a time shorter than the thermal relaxation time of the follicle, and
delivering sufficient energy fluence to generate a destructive temperature rise. The choice of wavelength defines penetration depth and determines applicability based on hair type and skin phototype.
Application areas
Laser hair removal applies to hair elimination across the entire body (face, legs, underarms, pubic area, chest) with efficacy varying according to location, hair type, phototype and technology used. Optimal results are achieved on thick, dark hair. Efficacy decreases on fine, white or very light hair. Aesthetic applications predominate, but therapeutic applications exist (hirsutism, pseudofolliculitis).
Frequently asked questions
The laser emits a specific monochromatic wavelength, while IPL produces a broad spectrum. Lasers offer greater precision and control, with better efficacy on dark phototypes according to recent clinical studies.
Generally 6 to 12 sessions spaced 4 to 8 weeks apart, depending on hair type and technology. Studies show a 57.9% reduction after 3 sessions and up to 70-80% after 12 months with 808nm diodes.
No. Ruby and Alexandrite lasers are suitable for phototypes I-III. 808/940nm diodes and Nd:YAG better tolerate dark phototypes (III-VI). The choice of technology depends on skin phototype to minimize risks.
Adverse effects include transient erythema, edema, burns, depigmentation, post-inflammatory hyperpigmentation and scarring. Skin preparation, technical parameters and phototype influence the risk of side effects.
Laser hair removal targets the active follicular germ (anagen phase). Hairs in the telogen phase are resistant. Progressive regrowth reflects the natural hair cycle and may require periodic maintenance sessions.
Studies classify laser hair removal as 'permanent reduction' rather than 'definitive elimination'. A lasting reduction of 70-90% is documented, with possible fine and slight regrowth of residual or dormant hairs.
808nm diodes and Alexandrite offer the best efficacy/safety/versatility balance for the majority of patients. For phototype VI, long-pulsed Nd:YAG lasers are preferred despite lower efficacy, for safety reasons.
Sources scientifiques
- Anderson RR, Parrish JA. Selective photothermolysis. Science (1983) ;220 (4596) :524-527 . PMID: 6836297
- Altshuler GB et al.. Extended theory of selective photothermolysis. Lasers Surg Med (2001) ;29 (5) :416-432 . PMID: 12030874
- Haedersdal M, Wulf HC. Evidence-based review of hair removal using lasers and light sources. J Eur Acad Dermatol Venereol (2006) ;20 (1) :9-20 . PMID: 16405602
- Gan SD, Graber EM. Laser hair removal: a review. Dermatol Surg (2013) ;39 (6) :823-838 . PMID: 23332016
- Ibrahimi OA et al.. Laser hair removal. Dermatol Ther (2011) ;24 (1) :94-107 . PMID: 21276162
- Goldberg DJ. Laser hair removal. Dermatol Clin (2002) ;20 (3) :561-567 .
- Casey AS, Goldberg D. Guidelines for laser hair removal. J Cosmet Laser Ther (2008) ;10 (1) :24-33 . PMID: 18330795
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