The primary mechanism of the 755nm Alexandrite laser is the targeted conversion of light energy into thermal energy within the hair follicle. The laser emits a specific wavelength of light (755nm) that is absorbed by melanin within the hair shaft. This absorbed energy generates intense heat, which is conducted down to the hair follicle and the bulge area, destroying the reproductive structures required for hair growth.
The core principle at work is selective photothermolysis. The laser utilizes the melanin in the hair shaft as a "lightning rod" to capture energy and deliver heat precisely to the follicle root, permanently disabling it while leaving the surrounding skin tissue unharmed.
The Science of Selective Photothermolysis
To understand how the Alexandrite laser achieves long-term results, one must understand the interaction between light and biological tissue.
Targeting the Chromophore
The 755nm wavelength is specifically tuned to target melanin, the pigment that gives hair its color. In laser physics, this target is known as a chromophore.
Because the Alexandrite laser has a high affinity for melanin, it ignores the water and blood in the skin, focusing almost entirely on the pigmented hair shaft.
Energy Conversion
When the laser light hits the melanin, a rapid physical transformation occurs. The light energy is instantaneously absorbed and converted into thermal energy (heat).
This is not a gradual warming process; it is a rapid spike in temperature designed to cause immediate structural damage to the target.
The Process of Follicle Destruction
The destruction of the hair is a multi-step thermal event initiated by the absorption of light.
Thermal Conduction
Once the melanin in the hair shaft absorbs the energy, the heat does not stay there. It is conducted outward from the hair shaft into the surrounding follicle structures.
This includes the bulge area and the germinative tissues (stem cells) responsible for regenerating hair.
Structural Elimination
The heat must be sufficient to damage the follicle beyond repair. The thermal damage effectively destroys the stem cells in the hair bulb.
In many cases, these functional tissues are replaced by non-functional connective tissue, preventing the follicle from producing a new hair shaft in the future.
Understanding the Trade-offs
While the 755nm Alexandrite laser is highly effective, its mechanism relies heavily on the presence of melanin, which introduces specific limitations.
Skin Tone Sensitivity
Because the laser targets melanin so aggressively, it struggles to distinguish between melanin in the hair and melanin in the skin.
This makes the 755nm wavelength risky for darker skin types (Fitzpatrick IV-VI), as the skin may absorb too much energy, leading to burns or hypopigmentation.
Requirement for Contrast
The mechanism requires a contrast between the hair and the skin.
It is most effective on patients with lighter skin and darker hair. It cannot effectively treat white, grey, or very blonde hair because there is insufficient melanin to act as a chromophore for the laser energy.
Making the Right Choice for Your Goal
The 755nm Alexandrite laser is a precision tool that excels in specific scenarios but requires careful patient selection.
- If your primary focus is treating light-to-olive skin tones: This laser is often the gold standard due to its high melanin absorption and ability to target finer hair textures.
- If your primary focus is speed on large body areas: The system's ability to use large spot sizes and high repetition rates makes it highly efficient for backs, legs, and chests.
- If your primary focus is safety on dark skin: You should likely consider a different wavelength (such as Nd:YAG), as the Alexandrite's high melanin affinity poses a higher risk of epidermal damage.
The 755nm Alexandrite laser remains a core technology for hair removal because it efficiently balances deep penetration with aggressive targeting of the hair's reproductive center.
Summary Table:
| Feature | Description |
|---|---|
| Wavelength | 755nm (Alexandrite) |
| Primary Target | Melanin (Chromophore) |
| Core Principle | Selective Photothermolysis |
| Energy Conversion | Light energy to thermal energy (heat) |
| Best Skin Types | Fitzpatrick I-III (Light to Olive) |
| Effective On | Dark, pigmented hair and fine textures |
| Primary Benefit | High absorption for rapid follicle destruction |
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References
- Azzam Alkhalifah. A Case Report of Vitiligo Induced by Alexandrite Hair Removal Laser. DOI: 10.1159/000520540
This article is also based on technical information from Belislaser Knowledge Base .
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