The 940nm wavelength provides a critical safety buffer for Fitzpatrick IV-VI skin types by utilizing a longer light wave that is less attracted to the pigment on the skin's surface.
Because 940nm is longer than the standard 810nm diode wavelength, it exhibits a lower absorption rate by epidermal melanin. This allows the energy to pass through the dark, melanin-rich surface of the skin without creating excessive heat, ensuring the energy is delivered safely to the deeper hair follicle.
Core Takeaway The safety of the 940nm wavelength lies in its ability to bypass surface pigment. By reducing epidermal absorption, it allows practitioners to use higher energy levels (fluence) to effectively treat hair follicles in dark skin without the risk of surface burns or hyperpigmentation associated with shorter wavelengths.
The Challenge of Melanin in Dark Skin
The Epidermis as a Barrier
In Fitzpatrick skin types IV-VI, the epidermis (the outer layer of skin) is rich in melanin. In laser hair removal, this presents a significant challenge because standard lasers target melanin to generate heat.
The Risk of Competitive Absorption
If a wavelength is too short, the melanin in the skin absorbs the energy before it reaches the hair root. This is known as competitive absorption.
Instead of destroying the follicle, the energy heats the skin's surface, leading to burns, blistering, or post-inflammatory hyperpigmentation.
How 940nm Enhances Safety
Lower Absorption Coefficient
The 940nm wavelength is longer than the industry-standard 810nm wavelength. As the wavelength increases, the absorption by melanin generally decreases.
This reduced affinity for melanin means the 940nm laser is less likely to "see" or react with the pigment located in the epidermis of dark skin.
Enabling Higher Fluence (Energy Density)
Because the skin surface absorbs less energy, the risk of thermal damage to the epidermis is significantly lowered.
This safety margin allows operators to increase the fluence (energy density). They can deliver a more powerful pulse to heat the deep hair follicle effectively without exceeding the skin's thermal relaxation time.
Deep Follicle Targeting
Dark skin types often require lasers that can penetrate deeply to ensure the energy is deposited in the dermis, not the epidermis.
The 940nm wavelength offers sufficient penetration depth to reach the hair bulb while sparing the skin surface, striking a balance between the shallower 810nm and the deeper 1064nm wavelengths.
Understanding the Trade-offs
The Spectrum of Safety
While 940nm is safer than 810nm for dark skin, it is important to understand where it fits in the broader spectrum.
Shorter wavelengths like 755nm (Alexandrite) have very high melanin absorption and pose the highest risk for dark skin.
Longer wavelengths like 1064nm (Nd:YAG) have the lowest melanin absorption and bypass the epidermis almost entirely, making them the traditional gold standard for the darkest skin tones (Type VI).
The 940nm Position
The 940nm wavelength functions as a bridge. It offers better safety than the 810nm diode but retains higher melanin absorption than the 1064nm Nd:YAG.
Operators must still exercise caution and proper cooling techniques, as there is still some melanin absorption compared to the purely "color-blind" nature of very long wavelengths.
Making the Right Choice for Your Goal
When selecting a wavelength for dark skin (Fitzpatrick IV-VI), consider the specific balance of safety and aggression required.
- If your primary focus is Maximum Safety for Type VI: The 1064nm Nd:YAG remains the safest option as it bypasses epidermal melanin almost completely to minimize burn risk.
- If your primary focus is Enhanced Diode Efficacy: The 940nm wavelength is ideal for treating Type IV and V skin, allowing for higher energy settings than a standard 810nm laser without the same surface risks.
- If your primary focus is Versatility: A device combining 810nm and 940nm allows for customization, treating lighter skin with 810nm and switching to 940nm for darker tones to maintain safety.
The 940nm wavelength empowers operators to treat dark skin with the high energy required for results, without the high risk of surface damage.
Summary Table:
| Feature | 755nm (Alexandrite) | 810nm (Diode) | 940nm (Diode) | 1064nm (Nd:YAG) |
|---|---|---|---|---|
| Melanin Absorption | Very High | High | Moderate | Low |
| Skin Type Suitability | Fitzpatrick I-III | Fitzpatrick I-IV | Fitzpatrick IV-V | Fitzpatrick V-VI |
| Safety for Dark Skin | Low Risk of Burns | Moderate Risk | Enhanced Safety | Maximum Safety |
| Penetration Depth | Shallow | Medium | Deep | Very Deep |
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References
- Viktoriia Chernychko. Specifics of using diode lasers on different skin and hair types. DOI: 10.5281/zenodo.17980578
This article is also based on technical information from Belislaser Knowledge Base .
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