The technical rationale for setting a pulse width between 10 and 40 milliseconds lies in optimizing the principle of selective photothermolysis to differentiate between the hair follicle and the surrounding skin.
A pulse duration in this specific range allows sufficient time for thermal energy to accumulate within the hair follicle to achieve destruction, while simultaneously allowing the epidermis to dissipate heat, thereby preventing burns and mechanical damage.
Core Takeaway The 10–40 millisecond window exploits the difference in cooling rates between skin and hair follicles. By keeping the pulse duration longer than the skin’s thermal relaxation time but shorter than that of the follicle, you maximize follicular damage while minimizing the risk of epidermal injury, particularly in patients with darker skin tones.
The Physics of Thermal Relaxation
Understanding Thermal Relaxation Time (TRT)
To destroy a target without damaging surrounding tissue, the laser pulse duration must ideally match the target's Thermal Relaxation Time (TRT).
Hair follicles are relatively large structures with a long TRT. This means they retain heat for a longer period.
A pulse width of 10 to 40 milliseconds is long enough to allow heat to build up continuously within the follicle, raising the temperature of germinative cells to the coagulation point.
The Differential Cooling Mechanism
While the follicle retains heat, the epidermis (the outer skin layer) cools down much faster.
When the pulse width is extended to the 10–40ms range, it exceeds the TRT of the epidermis.
This allows the skin to transfer absorbed heat into the surrounding air or cooling gel during the laser pulse, effectively protecting the epidermis while the follicle continues to cook.
Safety and Efficacy Mechanics
Avoiding Photoacoustic Damage
Extremely short pulses deliver energy so rapidly that they create a mechanical shockwave, known as a photoacoustic effect.
This can cause explosive vaporization and tissue tearing.
The 10–40ms "Long Pulse" mode delivers energy slowly enough to bypass these mechanical wave effects, resulting in purely thermal (heat-based) damage that is controlled and predictable.
Protection for Darker Skin Tones
For patients with higher epidermal melanin content, rapid heating is dangerous.
Short pulses heat epidermal melanin instantly, often leading to burns or hypopigmentation.
Utilizing the upper end of the 10–40ms range slows the rate at which epidermal melanin heats up. This slower heating rate significantly increases the safety margin for darker skin types.
Understanding the Trade-offs
The Risk of Pulse Widths That Are Too Long
If the pulse width extends significantly beyond the 40ms mark (or the specific TRT of the target hair), the heat begins to dissipate from the follicle into the surrounding dermis.
This reduces the peak temperature inside the follicle, potentially rendering the treatment ineffective.
It also risks non-specific heating of the surrounding nerve endings, increasing patient pain without improving efficacy.
The Risk of Pulse Widths That Are Too Short
Dropping significantly below this range (e.g., into the microsecond domain) increases the risk of epidermal injury.
The skin does not have adequate time to cool down during the energy delivery.
This forces the practitioner to use lower fluence (energy) levels to maintain safety, which often compromises the permanence of the hair reduction.
Making the Right Choice for Your Goal
When adjusting parameters within the 10–40ms window, consider the patient's physiology and hair type.
- If your primary focus is treating darker skin types (Fitzpatrick IV-VI): Lean toward the 30–40ms range to slow the heating of epidermal melanin and maximize safety.
- If your primary focus is treating fine or lighter hair: Lean toward the 10–20ms range, as thinner hair shafts lose heat faster and require a slightly quicker energy delivery to sustain damage.
The 10–40ms pulse width is the definitive technical "sweet spot" that transforms the Alexandrite laser from a superficial heater into a precise, follicle-destroying tool.
Summary Table:
| Parameter Range | Primary Target/Focus | Mechanism of Action | Clinical Benefit |
|---|---|---|---|
| 10 - 20ms | Fine or light-colored hair | Faster energy delivery to match shorter TRT | Sustains damage in thinner hair shafts |
| 20 - 30ms | Medium hair / Standard types | Balanced thermal accumulation | Versatile efficacy for most patients |
| 30 - 40ms | Darker skin (Fitzpatrick IV-VI) | Slower heating of epidermal melanin | Maximizes safety; prevents burns/hypopigmentation |
Elevate Your Clinic’s Standards with BELIS Technology
Precision in pulse width is the difference between a routine treatment and superior clinical results. BELIS specializes in professional-grade medical aesthetic equipment designed exclusively for high-end clinics and premium salons.
Our advanced laser systems, including Long-pulse Alexandrite, Diode Hair Removal, and Pico lasers, are engineered to give practitioners the granular control needed over parameters like pulse duration and fluence. Beyond hair removal, our portfolio includes CO2 Fractional lasers, HIFU, Microneedle RF, and body sculpting solutions (EMSlim, Cryolipolysis) to help you offer a full spectrum of premium care.
Ready to upgrade your practice with industry-leading technology?
Contact BELIS Today to Request a Quote
References
- Zekayі Kutlubay. Alexandrite laser hair removal results in 2359 patients: A Turkish experience. DOI: 10.1080/14764170902984903
This article is also based on technical information from Belislaser Knowledge Base .
Related Products
- Clinic Use IPL and SHR Hair Removal Machine with Nd Yag Laser Tattoo Removal
- IPL SHR Hair Removal Machine for Permanent Hair Removal
- Diode Laser SHR Trilaser Hair Removal Machine for Clinic Use
- Diode Tri Laser Hair Removal Machine for Clinic Use
- Clinic Diode Laser Hair Removal Machine with SHR and Trilaser Technology
People Also Ask
- Can you use a hair removal device on private parts? A Safe Zone Guide for Intimate Areas
- Does hair removal work better than shaving? Get Smoother, Longer-Lasting Results
- Can you see results after 1 IPL? What to Expect from Your First Treatment
- What are the negative effects of IPL? Understanding Risks for Safe Treatment
- How much do IPL treatments cost? A Guide to Investing in Clear, Smooth Skin
