The primary target of medical-grade long-pulse Alexandrite 755nm laser systems is the melanin pigment located within the hair follicle. Because the 755nm wavelength is highly absorbed by melanin, the system can selectively deliver energy to the hair root, converting light into heat to destroy the follicle structure while sparing the surrounding tissue.
Core Takeaway The Alexandrite 755nm laser relies on the principle of selective photothermolysis, using melanin as a "chromophore" (target) to absorb light energy. This precise interaction creates localized heat that disables the hair's germinative center, offering a highly effective long-term reduction solution, particularly for patients with lighter skin types.
The Science of Precision Targeting
The Role of Melanin
In the context of laser hair removal, melanin acts as the conductor for the laser's energy. The 755nm wavelength is specifically chosen because it falls within a spectrum where melanin absorption is exceptionally high compared to other tissue components.
Converting Light to Thermal Energy
Once the laser light penetrates the skin and strikes the melanin in the hair shaft and bulb, the energy is instantly converted. This conversion from light to thermal energy creates a rapid rise in temperature within the follicle.
Destruction of the Germinative Center
The objective is not merely to burn the hair shaft, but to transmit enough heat to the germinative center of the follicle. By damaging these regenerative tissues, the laser effectively inhibits the follicle's capacity to produce new hair in the future.
The Core Principle: Selective Photothermolysis
Defining the Mechanism
The entire process operates on selective photothermolysis. This is the concept of using a specific wavelength of light to thermally destroy a specific target (the hair follicle) without damaging the surrounding "non-target" tissue (the skin).
The Critical Role of Pulse Width
Precision is not just about wavelength; it is also about time. The laser's pulse width is calibrated to sit between the thermal relaxation times of the epidermis (skin) and the hair follicle.
Confining Thermal Damage
By optimizing the pulse width, the system ensures the hair follicle retains heat long enough to be destroyed. Simultaneously, it allows the surrounding skin to cool down, minimizing non-specific thermal damage to the epidermis.
Understanding the Trade-offs
Skin Type Sensitivity
Because the Alexandrite 755nm laser is so aggressively absorbed by melanin, it presents a challenge for darker skin tones which have high epidermal melanin content. These systems are most effective and safe for lighter skin types, as there is a clearer distinction between the hair color and the background skin color.
Managing Epidermal Heat
While the target is deep, the laser must pass through the surface of the skin. To prevent surface burns, these systems often employ contact cooling (such as sapphire handpieces) or chilled gels.
Dependence on Contrast
The efficacy of this specific wavelength drops if there is insufficient contrast between the hair and the skin. White, gray, or very blonde hair lacks the necessary melanin target, rendering the 755nm laser largely ineffective for those hair colors.
Making the Right Choice for Your Goal
To maximize clinical outcomes, it is essential to align the technology's strengths with the patient's specific profile.
- If your primary focus is treating lighter skin types (Fitzpatrick I-III): The high melanin absorption of the 755nm wavelength offers the most efficient and aggressive hair removal profile available.
- If your primary focus is treating darker skin types (Fitzpatrick IV-VI): You should exercise extreme caution with Alexandrite lasers and consider alternative wavelengths (like Nd:YAG) to avoid epidermal damage due to melanin competition.
- If your primary focus is patient comfort and safety: Ensure the system utilizes adequate epidermal cooling mechanisms, such as sapphire tips or chilled gels, to offset the high energy absorption at the surface.
Success with Alexandrite lasers requires respecting the precise relationship between the 755nm wavelength and the melanin target.
Summary Table:
| Feature | Alexandrite 755nm Specification |
|---|---|
| Primary Target | Melanin pigment in the hair follicle |
| Mechanism | Selective Photothermolysis |
| Best Skin Types | Fitzpatrick I - III (Light to Medium) |
| Core Benefit | High absorption for rapid, effective hair reduction |
| Safety Measure | Integrated cooling (Sapphire/Cryo) to protect epidermis |
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References
- Fatemeh Moeineddin, Reza M. Robati. Angiokeratoma of Fordyce—A rare complication of laser hair removal: A case report of two patients. DOI: 10.1002/ccr3.9077
This article is also based on technical information from Belislaser Knowledge Base .
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