The 590 to 1200 nm waveband is specifically selected to optimize the balance between melanin absorption and deep tissue penetration. This broad spectrum allows the light energy to successfully target the high melanin content in dark hairs while traveling deep enough into the dermis to destroy the roots of coarse, deep-seated lumbosacral hair.
Core Takeaway The 590–1200 nm range provides superior clinical adaptability by combining the light absorption necessary to heat dark hair shafts with the longer wavelengths required to reach deep hair bulbs. This effectively treats conditions involving coarse, deep terminal hairs—such as Faun Tail Naevus—where single, short-wavelength lasers often fail to penetrate sufficiently.
The Physics of Penetration and Absorption
Balancing Depth and Detection
Effective hair removal requires a specific trade-off. The light must be absorbed by the melanin (pigment) in the hair, but it must also pass through the skin to reach the follicle.
Why 590 nm?
The lower end of this spectrum (around 590 nm) targets melanin aggressively. This ensures that the light energy is "picked up" by the dark pigment within the hair shaft, converting that light into thermal energy.
Why 1200 nm?
The upper end of the spectrum (up to 1200 nm) is critical for depth. Longer wavelengths scatter less in tissue, allowing the energy to penetrate the deep dermis. Without this upper range, the energy would dissipate in the upper skin layers, failing to disable the reproductive center of deep hair follicles.
Addressing Coarse, Deep-Seated Hair
The Lumbosacral Challenge
Hairs in the lumbosacral region, particularly in conditions like Faun Tail Naevus, are classified as coarse terminal hairs. Unlike fine body hair, these follicles are anchored deeply within the skin.
Overcoming Depth Barriers
Standard short-wavelength lasers often lack the penetration depth to reach these specific hair bulbs. The 590–1200 nm broad-spectrum IPL system ensures the thermal damage occurs at the germinative center of the follicle, preventing regrowth.
High Melanin Efficiency
Because these coarse hairs are high in melanin, they act as excellent conductors for this specific waveband. The system relies on selective photothermolysis, where the hair actively absorbs the heat while the surrounding tissue remains largely unaffected.
The Importance of Pulse Control
Matching Thermal Relaxation
Penetration is only half the battle; retention of heat is the other. Coarse hairs have a longer thermal relaxation time, meaning they hold onto heat longer than the skin does.
Preventing Instant Evaporation
IPL systems allow for adjustable pulse durations (typically 5ms to 40ms). By using a longer pulse within this waveband, the system heats the hair shaft slowly and uniformly.
Heating the Germinal Cells
This controlled heating allows thermal energy to conduct outward from the hair shaft to the surrounding stem cells (germinal cells). This destroys the follicle thoroughly without causing the hair shaft to instantly vaporize, which would cut off the heat transfer before the root is killed.
Understanding the Trade-offs
Specificity vs. Versatility
While this waveband is highly effective for dark, coarse hair, it relies heavily on the presence of melanin. It is less effective on light, grey, or red hair where the target chromophore (melanin) is absent.
Optical Scattering
Even with the 1200 nm upper limit, light scatters as it enters tissue. To counteract this, large spot size technology is often used. A larger beam reduces scattering loss, driving the energy deeper, but it requires precise handling to ensure uniform coverage across large areas like the back.
Making the Right Choice for Your Goal
When evaluating light-based therapies for lumbosacral hair, consider the specific nature of the hair growth.
- If your primary focus is treating deep, coarse hair (e.g., Faun Tail Naevus): Prioritize the 590–1200 nm IPL range for its ability to penetrate to the deep dermis and effectively heat the hair bulb.
- If your primary focus is treating fine or surface-level hair: A system with a shorter wavelength or lower penetration depth may be sufficient, as deep dermal heating is less critical.
Success in treating coarse lumbosacral hair relies on delivering energy deep enough to destroy the root, not just burning the shaft at the surface.
Summary Table:
| Feature | 590 nm (Lower Bound) | 1200 nm (Upper Bound) |
|---|---|---|
| Primary Role | Aggressive melanin absorption | Deep tissue penetration |
| Target Area | Hair shaft pigment (chromophore) | Deep dermis & follicle bulbs |
| Effect | Converts light to thermal energy | Reaches germinative cells |
| Hair Type | High-melanin dark hair | Coarse terminal hairs |
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References
- Hye In Lee, Myeung Nam Kim. A Case of Faun Tail Naevus Treated by Intense Pulsed Light. DOI: 10.5021/ad.2009.21.2.147
This article is also based on technical information from Belislaser Knowledge Base .
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