The primary mechanism of action for the 755 nm Alexandrite Laser is selective photothermolysis. The device emits a specific wavelength of light (755 nm) that targets the melanin found within the hair follicle and shaft. This light energy is instantaneously converted into heat, creating thermal damage that expands the follicle unit and destroys the progenitor stem cells responsible for regeneration.
Core Takeaway: The efficacy of the 755 nm Alexandrite Laser relies on the precise destruction of the hair follicle's reproductive structures—specifically the stem cells—by using melanin as a thermal conductor. This allows for long-term hair reduction while leaving the surrounding skin tissue unharmed.
The Physics of Follicle Destruction
Selective Photothermolysis
The foundational principle of this treatment is selective photothermolysis. This concept dictates that a specific wavelength of light can target a specific chromophore (in this case, melanin) without affecting other tissues. The laser delivers energy in a way that creates local destruction only where the target absorbs the light.
Conversion to Thermal Energy
When the 755 nm light hits the hair, the melanin absorbs the energy and converts it into intense heat. This conversion must happen quickly to be effective. The thermal energy is then conducted throughout the hair structure, traveling from the shaft down to the root.
Targeting Progenitor Stem Cells
The ultimate goal of this thermal transfer is not just to burn the hair, but to disable the machinery of hair growth. The heat destroys the progenitor stem cells located in the hair bulb and the follicular bulge. By eliminating these cells, the follicle loses its ability to regenerate hair.
Mechanical Expansion
According to the primary technical data, the rapid release of laser energy induces thermal damage that physically expands the hair follicle unit. This expansion is a marker of the structural disruption necessary to achieve long-term reduction.
Why the 755 nm Wavelength Matters
High Melanin Absorption
The 755 nm wavelength is chosen because it sits in a sweet spot of the light spectrum that offers an exceptional absorption rate for melanin. This high absorption ensures that the maximum amount of energy is captured by the hair structure rather than passing through it or scattering ineffective heat.
Deep Tissue Penetration
Despite its high absorption, this wavelength is long enough to penetrate deep into the dermis. It can reach the deep-seated structures of the hair follicle (the bulb and bulge) to ensure the heat is delivered exactly where the stem cells reside.
Pulse Width Modulation
The system utilizes long pulse widths, typically ranging from 2 ms to 100 ms. This duration is critical; it allows enough time for the hair to absorb the energy and conduct the heat to the follicle walls, ensuring the destruction of the surrounding reproductive structures.
Understanding the Trade-offs
Specificity and Side Effects
Because the laser aggressively targets melanin, there is a biological interaction with the skin. While generally safe, the process can cause transient reactions such as erythema (redness), skin pigmentation changes, or folliculitis. These are typically mild, but they are direct results of the thermal energy interacting with the tissue.
Comparison to Diode Lasers
It is important to note that while 800nm Diode lasers may use longer pulse widths, clinical comparisons suggest the 755 nm Alexandrite creates a different sensation. Patients often report that Diode lasers cause "deeper and more severe" pain, whereas the Alexandrite's specific energy delivery and cooling mechanisms may offer a different comfort profile despite its high energy absorption.
Making the Right Choice for Your Goal
- If your primary focus is efficiency on lighter skin tones: The 755 nm wavelength offers superior melanin absorption, making it a benchmark for high-contrast hair removal (dark hair on light skin).
- If your primary focus is minimizing deep-tissue discomfort: The energy delivery of the Alexandrite laser is often perceived as less painful than the deep ache associated with 800nm Diode systems.
- If your primary focus is safety: The system's ability to confine thermal damage to the follicle ensures that surrounding non-target tissues remain protected.
By understanding that this technology targets the biological "blueprint" of the hair—the stem cells—you can better appreciate why it remains a gold standard for long-term reduction.
Summary Table:
| Feature | 755 nm Alexandrite Laser Mechanism |
|---|---|
| Core Principle | Selective Photothermolysis |
| Target Chromophore | Melanin (High absorption rate) |
| Energy Conversion | Light energy to intense thermal energy |
| Primary Target | Progenitor stem cells in the bulb and bulge |
| Pulse Width Range | 2 ms to 100 ms for controlled heat conduction |
| Clinical Result | Follicular expansion and permanent hair reduction |
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References
- Günseli Şefika Pancar, Oznur Eyupoglu. The effects of 755 nm alexandrite laser on skin drynessand pruritus. DOI: 10.5114/ada.2020.93381
This article is also based on technical information from Belislaser Knowledge Base .
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