When treating pigmented lesions with picosecond or Q-switched (nanosecond) lasers, the ability to correctly judge the endpoint reaction is one of the most important clinical skills. Many practitioners adjust fluence based on whitening alone, but without understanding the mechanism of whitening, it’s easy to overtreat, burn the epidermis, and increase the risk of post-inflammatory hyperpigmentation (PIH).
In this guide, Mico Aes explains:
- Why whitening occurs
- How cavitation affects epidermal reactions
- Differences between picosecond and nanosecond pulse widths
- How to choose safe endpoint reactions for each lesion type
This article is designed for dermatologists, laser therapists, clinic owners, and distributors seeking deeper professional knowledge.
1. What Is the “Endpoint Reaction” in Pigment Laser Treatment?
In pigment-targeting lasers (pico & Q-switched), the typical endpoint for epidermal pigmented lesions is:
✔ Immediate whitening of the lesion
Long-pulse lasers may also treat pigment, but their endpoint appears differently—usually:
✔ Slight darkening after several minutes
The degree of whitening can vary:
- Light white
- Gray-white
- Frost-white
- Porcelain-white
The darker and more melanin-dense the lesion is, the more obvious the whitening becomes.
2. Why Does Whitening Occur? The Real Scientific Mechanism
Most whitening reactions are misunderstood. Whitening is not pigment turning white.
Whitening is an optical scattering effect produced by laser-induced vacuoles.
Here’s how it happens:
Step 1 — Laser absorption by melanin
Short-pulse lasers (ns and ps) deliver energy faster than thermal relaxation time.
Step 2 — Rapid thermoelastic expansion
Melanosomes heat instantly and expand.
Step 3 — Mechanical shockwave formation
This creates a powerful photoacoustic / photothermal-mechanical effect.
Step 4 — Cavitation and tissue disruption
Shockwaves rupture melanosomes and surrounding tissue, forming vacuoles in:
- Epidermis
- Dermal–epidermal junction (DEJ)
Step 5 — Light scattering
The vacuoles scatter incident light → the lesion appears white.
The bigger the vacuole, the whiter the reaction.
3. Picosecond vs Nanosecond Laser: Why Their Whitening Looks Different
A key factor in cavitation size is pulse width.
Nanosecond Lasers (Q-Switched)
- Produce larger cavitation vacuoles
- Stronger scattering
- Whitening is more obvious
- Frost-white appears easily
- Higher PIH risk if overtreated
Picosecond Lasers
- Create smaller vacuoles
- Whitening is milder → ideal endpoint = gray-white
- Frost-white suggests over-energy or excess overlapping
- Lower thermal injury but easier to overtreat with high fluence
This explains why manufacturers recommend:
✔ Pico ideal endpoint: Light gray-white
✘ Frost-white: NOT ideal for pico
4. Why You Must Avoid Frost-White with Picosecond Lasers
Frost-white during pico treatment indicates:
- Fluence too high
- Shockwave intensity excessive
- Cavitation too large
- Tissue damage increased
This significantly raises the risk of:
- PIH
- Prolonged erythema
- Micro-epidermal injury
- Scarring in sensitive skin types
For safe and effective pico treatment:
➡ Aim for light gray-white only.
5. Clinical Parameter Setting Principles for Pico & Q-Switched Lasers
✔ 1. Treat epidermal lesions conservatively
Especially solar lentigines and freckles—the most PIH-prone lesions.
✔ 2. Do not chase “one-session clearance”
High fluence may clear pigment faster, but PIH makes overall results worse.
✔ 3. Pico → small cavitation → choose lower energy
- Endpoint = pale gray-white
- Avoid multi-pass overlapping
✔ 4. Nano → stronger cavitation → customize per lesion
- Light white for solar lentigo
- Frost-white may be acceptable for pigment-rich lesions
- Reduce fluence in Fitzpatrick III–V patients
✔ 5. Understand melanin density control
When melanin is abundant, even low energy may produce strong whitening.
6. Summary: Choosing the Right Endpoint Reaction
| Laser Type | Cavitation Size | Ideal Endpoint | Avoid | PIH Risk |
|---|---|---|---|---|
| Picosecond | Small | Gray-white | Frost-white | Medium |
| Q-Switched (ns) | Large | Light white | Excessive frost-white | High |
| Long-pulse pigment lasers | Minimal | Slight darkening | None | Low |
Key Takeaways
- Whitening is caused by light scattering from epidermal vacuoles.
- Larger vacuoles → stronger scattering → whiter appearance.
- Picosecond lasers should not produce frost-white under correct settings.
- Choosing the right endpoint reaction is critical for preventing PIH.
- Nanosecond lasers require more caution in darker skin types.
Why Clinics Choose Mico Aes Pigment Lasers
As a trusted global manufacturer, Mico Aes provides professional-grade devices that help clinics achieve safer and more consistent pigment removal results:
✔ Stable medical-grade laser energy output
(755/1064/532nm pico, Q-switched, and hybrid systems available)
✔ Advanced beam homogenization
Reduces hot spots, lowers PIH risk.
✔ Proven clinical efficacy
Used by dermatology clinics, med spas, and distributors worldwide.
✔ Lifetime technical support
1-on-1 training + parameter guidance.
✔ OEM/ODM for distributors
Support for branding, manuals, marketing materials, and product customization.
Ready to Upgrade Your Laser Portfolio?
Whether you operate a clinic or distribute aesthetic devices, Mico Aes offers the latest in picosecond, Q-switched, and fractional laser technology.
📩 Website: https://micoaes.com/product-category/laser-tattoo-removal/
📞 WhatsApp: +86 18506287248
🌍 Global Shipping | CE/FDA/ISO Certified | OEM & Distributor Support
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