The selection of laser wavelengths for hair removal is dictated by the principle of melanin absorption. For lighter skin (Fitzpatrick types I-III), the 755nm Alexandrite laser is chosen because its high melanin absorption rate effectively targets dark hair against a pale background. Conversely, for darker skin (Fitzpatrick types IV-V), the 1064nm Nd:YAG laser is the required standard; its longer wavelength bypasses the melanin in the skin's surface, penetrating deeper to target the hair follicle without causing surface burns.
The Core Takeaway The goal of laser hair removal is to heat the hair follicle without heating the skin. The choice of wavelength is a safety calculation: use 755nm for maximum efficacy on light skin, and 1064nm to ensure maximum safety on dark skin by avoiding epidermal damage.
The Physics of Skin Interaction
To understand why specific wavelengths are chosen, you must understand how laser energy interacts with pigment (melanin) in the skin versus the hair.
755nm (Alexandrite): High Melanin Affinity
The 755nm wavelength has a very high absorption rate for melanin. Because it is so readily absorbed by pigment, it is incredibly efficient at destroying hair follicles.
However, this high affinity creates a risk. If the skin itself contains significant melanin (darker skin tones), the laser cannot distinguish between the hair and the skin. This can lead to surface burns or hyperpigmentation. Therefore, this wavelength is optimized for light skin tones with dark hair.
1064nm (Nd:YAG): Deep Penetration
The 1064nm wavelength behaves differently; it has a lower affinity for melanin and a longer wavelength. This allows the light to travel past the melanin-rich upper layer of the skin (epidermis) without being fully absorbed.
Instead of burning the surface, the energy penetrates deeper into the dermis to reach the hair root. This makes it the preferred choice for darker skin types, as it effectively "ignores" the skin's natural pigment while still heating the hair follicle.
Aligning Wavelengths with the Fitzpatrick Scale
Professionals use the Fitzpatrick skin type scale to standardize these decisions.
Fitzpatrick Types I–III (Light Skin)
Patients in this category have fair to beige skin that burns easily or tans gradually. The 755nm Alexandrite laser is the gold standard here.
Because there is little competition from skin pigment, the laser can deliver high energy directly to the hair. This results in highly effective destruction of the follicle root.
Fitzpatrick Types IV–V (Dark Skin)
Patients in this category have olive, light brown, or dark brown skin. The 1064nm Nd:YAG laser is the critical choice for safety.
Using a 755nm laser on these skin types would cause the skin to absorb too much heat. The 1064nm option minimizes heat accumulation in the epidermis, significantly lowering the risk of adverse effects like burns.
Critical Trade-offs: Beyond Wavelength
While wavelength is the primary factor, successful treatment requires balancing other settings to ensure safety.
Pulse Duration and Heat Diffusion
Selecting the right wavelength is not enough; the speed of the laser pulse (pulse duration) matters.
For lighter skin, practitioners use shorter pulses (6–20 ms). This delivers energy quickly to "shock" and destroy the follicle.
For darker skin, the pulse duration is extended (15–34 ms). This slower delivery allows the skin time to cool down (thermal diffusion) between energy spikes, preventing the melanin in the skin from overheating while still destroying the hair.
Fluence (Energy Density)
The total energy delivered, known as fluence, must also be adjusted.
Lighter skin can generally tolerate higher energy densities (e.g., 12–22 J/cm²), ensuring aggressive hair destruction. Darker skin requires carefully reduced fluence to prevent the higher levels of epidermal melanin from absorbing excessive heat.
Making the Right Choice for Your Goal
When selecting a treatment plan or device, consider your skin type as the non-negotiable baseline for safety.
- If your primary focus is Efficacy on Light Skin (Type I-III): Prioritize the 755nm Alexandrite laser, as its high melanin absorption provides the most efficient hair destruction for your skin type.
- If your primary focus is Safety on Dark Skin (Type IV-V): You must insist on the 1064nm Nd:YAG laser to bypass surface pigment and avoid the high risk of burns associated with shorter wavelengths.
Ultimately, the correct wavelength is the one that destroys the hair follicle while leaving the surrounding skin completely unharmed.
Summary Table:
| Skin Type (Fitzpatrick) | Recommended Wavelength | Key Benefit | Typical Pulse Duration |
|---|---|---|---|
| Types I - III (Light) | 755nm Alexandrite | High melanin absorption for fast results | Short (6-20 ms) |
| Types IV - VI (Dark) | 1064nm Nd:YAG | Bypasses surface melanin to prevent burns | Long (15-34 ms) |
| Tanned Skin | 1064nm Nd:YAG | Enhanced safety for pigment-rich surfaces | Moderate to Long |
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References
- E. Victor Ross, Scott A. Davenport. Airborne particulate concentration during laser hair removal: A comparison between cold sapphire with aqueous gel and cryogen skin cooling. DOI: 10.1002/lsm.22772
This article is also based on technical information from Belislaser Knowledge Base .
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