The primary criteria for selecting between 755nm and 810nm wavelengths for axillary hair removal are the patient's skin phototype and the specific characteristics of the hair being treated. While the 755nm Alexandrite laser is the optimal choice for light skin with fine hair due to its high melanin absorption, the 810nm Diode laser is preferred for patients with darker skin tones and deep-seated follicles because of its deeper penetration and superior safety profile regarding epidermal melanin.
Effective laser hair removal requires a precise balance between maximizing damage to the hair follicle and minimizing injury to the surrounding skin. The choice of wavelength dictates this balance: 755nm offers aggressive surface-level absorption, while 810nm provides the depth and safety required for darker skin types and deeper roots.
Evaluating Skin Phototype
The most critical factor in wavelength selection is the amount of melanin present in the patient's epidermis.
High Safety for Darker Skin (810nm)
The 810nm Diode laser is characterized by lower selectivity for epidermal melanin compared to the 755nm wavelength.
This allows the laser energy to bypass the pigment in the upper layers of the skin. Consequently, it significantly reduces the risk of post-inflammatory hyperpigmentation, making it the safer option for patients with darker skin types, specifically those categorized as Fitzpatrick III-V.
Optimization for Lighter Skin (755nm)
The 755nm long-pulse Alexandrite laser possesses a very high melanin absorption rate.
This aggressive absorption makes it highly effective for lighter skin tones where there is little competition from epidermal melanin. However, this same characteristic makes it risky for darker skin, as the laser cannot easily distinguish between hair melanin and skin melanin, leading to potential burns.
Analyzing Hair Characteristics and Depth
The physical nature of the hair follicle—specifically its texture and depth—determines which wavelength will be most effective.
Targeting Fine Hair (755nm)
Because the 755nm wavelength is so strongly absorbed by melanin, it is exceptionally good at targeting structures with less pigment density.
This makes it the ideal candidate for treating fine hair that might otherwise be missed by lasers with lower absorption coefficients.
Targeting Deep, Terminal Hair (810nm)
Axillary hair often consists of dark, terminal hairs with roots capable of residing deep within the dermis.
The 810nm wavelength offers deeper penetration than the 755nm. This allows the energy to reach deep-seated follicles, effectively destroying the growth centers—specifically the Bulge and Bulb areas—located in the deep dermis and subcutaneous tissue.
Understanding the Trade-offs and Risks
While selecting the correct wavelength optimizes results, it is vital to understand the side effects associated with the mechanism of action, particularly regarding depth of penetration.
The Risk of Collateral Thermal Damage
The 810nm laser's ability to penetrate deep into the subcutaneous tissue is its greatest strength, but also a source of potential side effects.
Because the laser energy reaches the deep dermis, it may unintentionally activate or damage adjacent sweat gland fibers. This thermal damage is a primary physical factor contributing to post-operative hyperhidrosis (excessive sweating) in some patients.
Making the Right Choice for Your Goal
When finalizing your treatment plan, assess the patient's profile against these distinct capabilities.
- If your primary focus is treating light skin with fine hair: Prioritize the 755nm Alexandrite laser to maximize melanin absorption in hair structures that are difficult to heat.
- If your primary focus is safety for darker skin (Fitzpatrick III-V): Select the 810nm Diode laser to bypass epidermal melanin and minimize the risk of surface burns and hyperpigmentation.
- If your primary focus is deep follicle destruction: Utilize the 810nm wavelength to ensure thermal energy reaches the deep Bulge and Bulb growth centers of terminal hairs.
Select the wavelength that provides the highest efficacy for the hair depth while maintaining the strictest safety margin for the patient's specific skin type.
Summary Table:
| Feature | 755nm Alexandrite Laser | 810nm Diode Laser |
|---|---|---|
| Ideal Skin Type | Fitzpatrick I - II (Light skin) | Fitzpatrick III - V (Darker skin) |
| Hair Texture | Fine, thin hair | Coarse, terminal hair |
| Melanin Absorption | Very high (Surface level) | Moderate (Lower epidermal risk) |
| Penetration Depth | Shallow to Medium | Deep (Reaches Bulge & Bulb) |
| Primary Risk | Epidermal burns on dark skin | Potential deep thermal damage |
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References
- Josiane Hélou, Roland Tomb. Nouveaux effets indésirables du laser dépilatoire axillaire. DOI: 10.1016/j.annder.2009.04.005
This article is also based on technical information from Belislaser Knowledge Base .
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