The primary mechanism is selective photothermolysis utilizing a high melanin absorption coefficient. The 755nm long-pulse Alexandrite laser targets the melanin within the hair follicle, converting light energy into thermal energy to destroy the hair growth centers (the bulb and bulge). For Fitzpatrick skin types III-IV, the "long-pulse" aspect is critical: it extends the energy delivery time to allow the pigment-rich epidermis to dissipate heat, preventing burns while ensuring the follicle is destroyed.
Core Takeaway While the 755nm wavelength is highly effective due to its aggressive absorption by melanin, its use on Fitzpatrick types III-IV requires a delicate balance of extended pulse widths and strict cooling protocols. This combination ensures the laser targets the hair follicle without damaging the surrounding pigmented skin.
The Core Principle: Selective Photothermolysis
To understand why this laser is used, we must look at how it interacts with biology. The process relies on matching the laser's wavelength to a specific target, known as a chromophore.
Targeting the Chromophore
The 755nm wavelength is specifically chosen for its high absorption coefficient for melanin. Because melanin is the primary pigment in hair, the laser energy is naturally drawn to the hair shaft and follicle structure.
Thermal Destruction
Once absorbed, the light energy is instantly converted into heat. This thermal energy damages the stem cells located in the hair follicle's bulge and bulb areas. By destroying these growth centers, the laser effectively inhibits future hair regrowth.
Adapting for Fitzpatrick III-IV: The Safety Mechanisms
The challenge with Fitzpatrick skin types III-IV is that the epidermis (the skin's surface) also contains significant amounts of melanin. This creates "competitive absorption," where the skin competes with the hair for the laser's energy.
Managing Epidermal Melanin
In darker skin tones, the high melanin content in the epidermis creates a risk of collateral damage. If the laser energy is absorbed too quickly by the skin surface, it can cause burns or hyperpigmentation. The system must differentiate between the melanin you want to hit (the hair) and the melanin you want to save (the skin).
The Critical Role of Pulse Width
This is where the "long-pulse" designation becomes vital. By adjusting the pulse width (the duration the laser fires), practitioners can manipulate how heat is held in the tissue.
For darker skin (Fitzpatrick IV-V), the pulse width is extended (typically ranging toward 15 to 34 ms). This longer duration takes advantage of thermal relaxation time. It gives the epidermis time to dissipate heat safely, while the larger, coarser hair follicle continues to accumulate thermal energy to the point of destruction.
Strict Cooling Protocols
Alongside pulse duration, the primary reference emphasizes that strict cooling protocols are non-negotiable for these skin types. Contact cooling protects the epidermis by keeping it cold before, during, and after the laser pulse. This minimizes the risk of thermal injury to the skin surface without reducing the heat delivered to the deeper hair follicle.
Understanding the Trade-offs
While the long-pulse Alexandrite is effective, it is not without risks when applied to intermediate-to-dark skin tones.
The Margin for Error
Because the 755nm wavelength has such a high affinity for melanin, the margin for error on Fitzpatrick types III-IV is narrower than with other wavelengths (such as 1064nm Nd:YAG). Improper settings can lead to rapid temperature spikes in the epidermis.
Balancing Fluence and Pulse Width
There is a trade-off between energy density (fluence) and safety. To protect the skin, practitioners often must use longer pulse widths. However, if the pulse is too long without sufficient energy, the follicle may not reach the temperature required for permanent destruction, leading to suboptimal results.
Making the Right Choice for Your Goal
Successful treatment relies on customizing the laser parameters to the specific patient's physiology.
- If your primary focus is Safety on Darker Skin (Type IV): Prioritize longer pulse widths (approx. 30-34ms) and aggressive cooling to allow epidermal heat dissipation.
- If your primary focus is Efficacy on Lighter Skin (Type III): You may utilize slightly shorter pulse widths to generate rapid thermal damage, provided contact cooling remains constant.
- If your primary focus is Fine Hair Removal: The 755nm wavelength is superior to longer wavelengths (like 800nm or 1064nm) because its high melanin absorption allows it to "grab" lighter, finer hairs effectively.
Ultimately, the 755nm Alexandrite laser is a powerful tool for Fitzpatrick III-IV skin only when the operator strictly manages thermal relaxation through extended pulse durations and aggressive surface cooling.
Summary Table:
| Feature | Mechanism/Parameter | Benefit for Fitzpatrick III-IV |
|---|---|---|
| Wavelength | 755nm Alexandrite | High melanin absorption for effective hair follicle destruction. |
| Core Principle | Selective Photothermolysis | Targets hair melanin while sparing surrounding tissue. |
| Pulse Width | Long-pulse (15-34 ms) | Allows epidermal heat dissipation via thermal relaxation time. |
| Safety Protocol | Aggressive Cooling | Protects the skin surface from burns and hyperpigmentation. |
| Target Area | Bulb and Bulge | Permanent inhibition of future hair regrowth. |
Elevate Your Clinic’s Precision with BELIS Medical Systems
For clinics and premium salons catering to diverse skin tones, achieving the perfect balance between efficacy and safety is paramount. BELIS specializes in professional-grade medical aesthetic equipment, providing the advanced technology needed to treat Fitzpatrick types III-IV with confidence.
Our extensive portfolio includes:
- Advanced Laser Systems: High-performance Diode Hair Removal, CO2 Fractional, Nd:YAG, and Pico lasers.
- Precision Body Contouring: Industry-leading EMSlim, Cryolipolysis, and RF Cavitation devices.
- Specialized Skin Care: HIFU, Microneedle RF, Hydrafacial systems, and high-accuracy skin testers.
Maximize your ROI and patient satisfaction with BELIS. Our equipment is engineered for durability, safety, and superior clinical results.
Contact BELIS Today to Upgrade Your Equipment Portfolio
References
- Hye‐Rim Moon, Jeesoo An. Long-pulsed Alexandrite Laser vs. Intense Pulsed Light for Axillary Hair Removal in Korean Women. DOI: 10.25289/ml.2012.1.1.11
This article is also based on technical information from Belislaser Knowledge Base .
Related Products
- Diode Tri Laser Hair Removal Machine for Clinic Use
- Clinic Diode Laser Hair Removal Machine with SHR and Trilaser Technology
- Clinic Use IPL and SHR Hair Removal Machine with Nd Yag Laser Tattoo Removal
- Diode Laser SHR Trilaser Hair Removal Machine for Clinic Use
- Trilaser Diode Hair Removal Machine for Beauty Clinic Use
People Also Ask
- How does a diode laser facilitate hair removal? Master the Science of Selective Photothermolysis for Smooth Skin
- What are the primary safety measures for performing diode laser hair removal on dark skin types? Expert Safety Guide
- Why is the pulse duration parameter critical for thermal damage control? Master Laser Hair Removal Precision
- Why should clinics conduct detailed literature research before adopting new laser hair removal technologies?
- How does a large spot size, such as 20mm, affect laser hair removal? Master Deep Penetration and Clinical Efficiency
