The primary function of laser wavelengths between 700 and 1100 nm is to execute precise, selective thermal damage to the hair follicle. This specific spectral range exploits the high absorption properties of melanin, allowing light energy to penetrate deep into the dermis and concentrate strictly on the hair shaft and matrix. By focusing on melanin, these wavelengths effectively destroy the follicle structure while bypassing other skin components like water and blood.
The Core Insight: This spectral range acts as the skin's "optical window." It strikes the critical balance of maximizing heat absorption by the hair root while minimizing absorption by surrounding tissues, ensuring deep penetration without causing unnecessary surface injury.
The Mechanics of Selective Targeting
Utilizing Melanin as a Conductor
The efficacy of this wavelength range relies on selective photothermolysis. Melanin, the pigment found in hair, exhibits a very high absorption rate between 700 and 1100 nm. When the laser hits the hair, the melanin absorbs the light, converting it into intense heat that travels down the shaft to destroy the root.
Avoiding Competing Tissues
For a laser to be safe, it must ignore non-target tissues. In the 700 to 1100 nm range, competing chromophores—specifically oxyhemoglobin (blood) and water—have relatively weak absorption rates. This ensures the energy is not wasted heating the blood or skin moisture, which significantly reduces the risk of accidental injury or bruising.
Deep Dermal Penetration
Hair follicles are located deep within the subcutaneous tissue. Shorter wavelengths may be absorbed too close to the surface, failing to disable the hair permanently. The 700–1100 nm range penetrates deeply enough to reach the follicle root and matrix, delivering the thermal damage exactly where it is needed to prevent regrowth.
Wavelength Specifics and Efficacy
The "Gold Standard" Technologies
This specific band includes several industry-standard laser types. Common examples include the 755 nm Alexandrite, the 808 nm Diode, and the 1064 nm Nd:YAG systems. These are often used individually or in blended handles to treat various hair textures and depths comprehensively.
Safety for Diverse Skin Types
While melanin absorption is the goal, it presents a challenge for darker skin tones which have high epidermal melanin. Longer wavelengths in this range, particularly the 1064 nm Nd:YAG, offer a solution. They bypass surface melanin more effectively to target the deeper follicle, making them safer for darker skin types by avoiding surface burns.
Understanding the Trade-offs
The Risk of Misapplication
While this range is optimized for safety, using an inappropriate wavelength for a specific skin type remains a hazard. Incorrect settings can lead to burns, hyperpigmentation (darkening), or hypopigmentation (lightening). The laser must always match the patient's skin phenotype to distinguish between the melanin in the hair and the melanin in the skin.
The Necessity of Surface Preparation
The physics of these wavelengths requires that the energy be concentrated subcutaneously. If hair is too long (longer than 2–3 mm), the laser energy will be absorbed by the external hair shaft. This causes the hair to heat up instantly and fuse to the skin or the laser handpiece, creating sticky carbonized debris and significantly increasing the probability of thermal injury.
Making the Right Choice for Your Goal
Selecting the correct approach within this wavelength range depends on the specific patient profile and safety requirements.
- If your primary focus is safety on dark skin: Utilize longer wavelengths like the 1064 nm Nd:YAG, as it bypasses epidermal melanin to target the follicle without damaging the surface skin.
- If your primary focus is general efficacy on mixed skin types: Consider Diode laser systems (approx. 808 nm) or blended wavelength handles, as they offer a balance of deep penetration and melanin absorption for permanent results.
- If your primary focus is preventing surface injury: Ensure hair is shortened to a uniform length of 2 to 3 mm so the laser energy targets the subcutaneous root rather than the external shaft.
Successful hair removal relies on leveraging this specific optical window to deliver maximum heat to the follicle with minimum impact on the surrounding tissue.
Summary Table:
| Feature | Laser Wavelength Range (700 - 1100 nm) |
|---|---|
| Core Mechanism | Selective Photothermolysis (targeting melanin) |
| Key Chromophore | Melanin (high absorption) |
| Low Absorption | Water and Oxyhemoglobin (reduces skin/blood damage) |
| Common Systems | Alexandrite (755nm), Diode (808nm), Nd:YAG (1064nm) |
| Primary Goal | Deep dermal penetration to destroy the follicle root/matrix |
| Skin Safety | Long wavelengths (1064nm) are safer for darker skin tones |
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References
- H. H. Zenzie, Gregory B. Altshuler. Super long pulse hair removal. DOI: 10.1109/leos.2000.890749
This article is also based on technical information from Belislaser Knowledge Base .
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