A long pulse width ranging from 5 to 30 milliseconds is mechanically necessary to distinguish between the skin and the hair follicle during heating. This specific duration allows the laser to deliver enough thermal energy to destroy the hair root while simultaneously giving the skin's surface enough time to cool down.
The Core Principle: Laser safety relies on the "Thermal Relaxation Time" (TRT)—the time it takes for a target to cool by 50%. A 5-30ms pulse width exploits the difference in TRT between the skin (which cools quickly) and the hair follicle (which retains heat longer), preventing burns while ensuring effective treatment.
The Mechanics of Thermal Relaxation
To understand why this range is necessary, you must understand how heat behaves differently in the hair versus the skin.
Heat Accumulation in the Follicle
Hair follicles are relatively large structures. Their Thermal Relaxation Time typically lasts between 10 and 100 milliseconds.
Because they are large, they hold onto heat for a longer period. A pulse width of 5 to 30 milliseconds falls squarely within this window, allowing thermal energy to accumulate in the follicle until it reaches the temperature required for destruction.
Heat Dissipation in the Epidermis
The epidermis (the outer layer of skin) contains smaller melanin particles that heat up quickly but also cool down very fast.
By using a "long" pulse (milliseconds rather than nanoseconds), you allow the smaller epidermal particles to dissipate heat during the laser shot. This prevents the rapid temperature spikes that cause blistering or burns.
Adapting to Different Skin Types
The 5 to 30 millisecond range provides the adjustability required to treat the full spectrum of Fitzpatrick skin types safely.
Treating Light Skin (Fitzpatrick I-II)
Lighter skin has less epidermal melanin, meaning there is a lower risk of surface burns.
For these patients, the pulse width is typically set to the shorter end of the range, often 6 to 20 milliseconds. This delivers energy more aggressively to generate sufficient thermal damage within the follicle, which is often finer and lighter in color.
Treating Darker Skin (Fitzpatrick IV-VI)
Darker skin contains a high concentration of epidermal melanin, which competes with the hair for laser energy.
For these patients, the pulse width must be extended to the longer end of the range, generally 15 to 34 milliseconds. This slower release of energy acts as a safety valve; it ensures the epidermis has ample time to cool via thermal diffusion, while the larger hair follicle continues to absorb and retain the energy needed for its destruction.
Understanding the Trade-offs
While long pulse widths are a critical safety feature, understanding their limitations is vital for clinical success.
The Risk of Being Too Aggressive (Too Short)
If the pulse width is set too short (e.g., <5ms) on a patient with dark skin, the epidermal cooling mechanism fails. The melanin in the skin absorbs energy faster than it can release it, leading to pigmentation issues, burns, or blistering.
The Risk of Being Too Gentle (Too Long)
If the pulse width is extended too far beyond the thermal relaxation time of the hair (e.g., significantly exceeding the target's TRT), the follicle may cool down while it is being heated. This renders the treatment ineffective, as the target never reaches the lethal temperature required to destroy the germinal tissue.
Making the Right Choice for Your Goal
Selecting the precise pulse width within the 5 to 30ms range is a balancing act between safety and efficacy.
- If your primary focus is treating Fitzpatrick Skin Types I-II: Use shorter pulse widths (6–20 ms) to aggressively target the follicle, as the skin requires less thermal protection.
- If your primary focus is treating Fitzpatrick Skin Types IV-VI: Use longer pulse widths (15–30 ms) to allow epidermal heat dissipation, ensuring the surface remains cool while the follicle is destroyed.
Ultimately, the 5-30ms pulse width gives you the necessary control to maximize follicular damage while minimizing epidermal risk.
Summary Table:
| Skin Type (Fitzpatrick) | Recommended Pulse Width | Thermal Mechanism | Goal |
|---|---|---|---|
| Types I-III (Light) | 6 – 20 ms | Faster delivery | Aggressive follicle destruction |
| Types IV-VI (Dark) | 15 – 34 ms | Slower delivery | Maximum epidermal cooling & safety |
| Target: Follicle | 10 – 100 ms TRT | Heat accumulation | Permanent hair reduction |
| Target: Epidermis | < 1 ms TRT | Heat dissipation | Prevention of burns & blisters |
Elevate Your Clinic’s Precision with BELIS Medical Technology
At BELIS, we specialize in professional-grade medical aesthetic equipment designed exclusively for clinics and premium salons. Our advanced Diode Laser systems, Nd:YAG, and Pico lasers provide the precise pulse width control necessary to treat all Fitzpatrick skin types safely and effectively.
Why partner with BELIS?
- Versatility: From high-performance laser hair removal and HIFU to Microneedle RF and body sculpting (EMSlim, Cryolipolysis).
- Safety: Advanced cooling technologies that complement optimal pulse width settings for maximum patient comfort.
- Comprehensive Care: Expand your services with our specialized skin testers, Hydrafacial systems, and hair growth machines.
Ready to upgrade your practice with industry-leading technology? Contact us today to request a quote or consultation and see how BELIS can deliver superior results for your clients.
References
- Valéria Campos, R. Rox Anderson. Hair removal with an 800-nm pulsed diode laser. DOI: 10.1067/mjd.2000.107239
This article is also based on technical information from Belislaser Knowledge Base .
Related Products
- Diode Tri Laser Hair Removal Machine for Clinic Use
- Trilaser Diode Hair Removal Machine for Beauty Clinic Use
- Clinic Diode Laser Hair Removal Machine with SHR and Trilaser Technology
- Diode Laser SHR Trilaser Hair Removal Machine for Clinic Use
- Clinic Use IPL and SHR Hair Removal Machine with Nd Yag Laser Tattoo Removal
People Also Ask
- How does extending the pulse duration protect dark skin? Master Safe Laser Hair Removal for Fitzpatrick Types IV-VI
- How does a large spot size, such as 20mm, affect laser hair removal? Master Deep Penetration and Clinical Efficiency
- Why is the pulse duration parameter critical for thermal damage control? Master Laser Hair Removal Precision
- How is high-resolution optical microscopy utilized in the clinical evaluation of laser hair removal? Scientific Metrics
- Why should clinics conduct detailed literature research before adopting new laser hair removal technologies?
