The 755 nm wavelength is selected primarily for its high affinity for melanin. This specific place in the light spectrum offers a "peak absorption" capability, allowing the laser to aggressively target the pigment within the hair follicle. Crucially, it balances this high absorption with sufficient penetration depth, ensuring the energy reaches the root of the hair without burning the surface of the skin.
The Core Mechanism The effectiveness of the 755 nm wavelength relies on selective photothermolysis. It delivers energy that is specifically absorbed by the hair's melanin to destroy the follicle's stem cells, while specific timing protocols prevent thermal damage to the surrounding epidermis.
The Principle of Selective Targeting
High Melanin Absorption
The 755 nm wavelength is engineered to match the peak absorption range of melanin. Because hair follicles contain a high concentration of this pigment, they act as "magnets" for this specific light energy.
Precise Energy Delivery
By focusing on this absorption peak, the laser differentiates between the hair and the skin. The energy is absorbed rapidly by the hair shaft, converting light into heat.
Minimal Surface Damage
Because the wavelength is so specific to the melanin in the follicle, it bypasses the majority of the surrounding skin tissue. This selectivity is the foundation of effective treatment with minimal side effects.
Achieving Permanent Reduction
Reaching the Follicular Unit
Absorption alone is not enough; the light must reach the source of growth. The 755 nm wavelength maintains sufficient penetration depth to travel through the upper layers of skin and strike the follicular unit.
Destroying Progenitor Stem Cells
Once the energy reaches the follicle, it induces thermal damage. This heat expands the follicular unit and destroys the progenitor stem cells. Eliminating these cells is essential for achieving long-term, permanent hair reduction rather than temporary removal.
Understanding the Trade-offs: Heat vs. Safety
The Challenge of Thermal Damage
Because the 755 nm wavelength generates heat so efficiently within melanin, there is a risk of that heat radiating outward into the skin. If the energy is released too quickly, the epidermis does not have time to cool down.
The Role of Pulse Width
To mitigate this risk, effective systems utilize a long pulse width, typically between 150 to 400 milliseconds (ms). This duration is designed to match the thermal relaxation time of the tissue.
Balancing Efficacy and Protection
Releasing energy gradually over this longer duration allows the epidermal layer (skin surface) to dissipate heat and cool down. Simultaneously, the hair follicle, which holds heat longer, accumulates enough energy to reach permanent functional failure.
Making the Right Choice for Your Goal
When evaluating laser technology for underarm hair reduction, the specifications determine the safety profile and the results.
- If your primary focus is treatment efficacy: Look for the 755 nm wavelength, as its position in the peak melanin absorption range ensures the most direct targeting of the hair follicle structure.
- If your primary focus is skin safety: Verify the device uses a long pulse width (150–400 ms), which is critical for allowing the skin to cool while the follicle is destroyed, preventing burns.
Ultimately, the 755 nm wavelength offers the optimal balance of depth and absorption to destroy hair stem cells while leaving the surrounding skin intact.
Summary Table:
| Feature | 755 nm Wavelength Performance |
|---|---|
| Primary Target | High affinity for Melanin (Selective Photothermolysis) |
| Penetration Depth | Optimal for reaching the follicular unit & stem cells |
| Pulse Width Range | 150 - 400 ms (Thermal relaxation management) |
| Key Benefit | Long-term permanent reduction with minimal surface damage |
| Ideal For | Effective targeting of pigmented hair in sensitive areas |
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References
- Azin Ayatollahi, Alireza Firooz. Comparison of efficacy and safety of a novel 755-nm diode laser with conventional 755-nm alexandrite laser in reduction of axillary hairs. DOI: 10.1007/s10103-019-02829-x
This article is also based on technical information from Belislaser Knowledge Base .
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