In professional laser dermatology, mastering the endpoint reaction is the key to delivering safe, precise, and effective pigment treatments. Whether using Pico lasers or Q-switched (nanosecond) lasers, understanding how the skin responds to energy exposure helps clinicians fine-tune parameters and prevent complications such as post-inflammatory hyperpigmentation (PIH).
However, many practitioners still rely on visual cues without fully understanding the optical and histological mechanisms behind whitening reactions. This often leads to inaccurate energy settings, overtreatment, or inconsistent results.
This guide explains the science, principles, and clinical techniques for interpreting and adjusting laser parameters according to visible endpoint reactions. By understanding the differences between gray-white, frost-white, and mild whitening effects—and knowing how they relate to pulse width, melanin absorption, and cavitation—clinicians can achieve optimal outcomes in pigment lesion removal and skin rejuvenation with both Pico and Q-switched lasers.
This manual summarizes the effective endpoint reactions during Pico/Nano laser, eyebrow tattoo removal, lip lightening, and carbon laser facial treatments. It aims to help operators accurately judge energy levels, control treatment depth, and prevent complications in clinical practice.
I. Pico/Nano Laser Treatment Endpoints
Applications: Used for benign pigmentary disorders such as freckles, melasma, nevus of Ota, and café-au-lait macules.
| Lesion Type | Wavelength Used | Ideal Endpoint Reaction | Notes |
| Freckles | 532/694/755 nm Q-switched | Immediate whitening (3–20 min) followed by darkening | 532 nm prone to purpura; avoid excessive energy |
| Melasma | 755/1064 nm low-energy mode | Mild erythema or no obvious change | Avoid whitening or purplish discoloration |
| Hori’s Nevus | 755/694 nm Q-switched | Immediate whitening | High energy may worsen pigmentation |
| Nevus of Ota | 755/1064/694 nm Q-switched | Immediate whitening, sometimes pinpoint bleeding | Control energy to avoid deep thermal damage |
| Lentiginous Nevus | 351–1064 nm | Immediate whitening or slight gray tone | Treat gradually to prevent PIH |
| Café-au-lait Spot | Q-switched/Pico/IPL/Fractional | Mild whitening or redness | Individualized protocol required |
Key Points: Aim for visible whitening without damage; whitening lasting 3–20 minutes is ideal; avoid scabbing modes; use multiple low-energy sessions.
II. Eyebrow Tattoo Removal
Device: 532 nm / 1064 nm Q-switched laser, Pico laser
Goal: Destroy pigment particles in the epidermis or superficial dermis.
| Reaction | Explanation | Energy Evaluation |
| Instant whitening | Pigment absorbs energy and vaporizes | Appropriate energy |
| Mild redness/swelling | Shallow tissue heating response | Normal |
| No bleeding | Safe operation | Optimal energy |
| Reddening or darkening after 10–30 min | Normal metabolic process | Within safe range |
⚠️ Abnormal endpoints: bleeding, exudation, carbonization, or purpura indicate excessive energy; reduce energy or enlarge spot size.
III. Lip Lightening (Dark Lip Treatment)
Device: 1064 nm Q-switched Nd:YAG or Pico laser
Goal: Break down melanin in the mucosa and superficial dermis.
| Reaction | Explanation | Energy Evaluation |
| Light grayish-white fog-like response | Energy absorbed by pigment, mild vaporization | Ideal endpoint |
| Slight redness/swelling | Normal mucosal response | Acceptable |
| No bleeding | Energy within safe range | Safe |
| Becomes light pink or slightly darker after a few minutes | Mild, self-limiting reaction | Stable |
⚠️ Abnormal: bleeding, thick scabbing, or prolonged swelling (>24h) indicate excessive energy; adjust parameters.
IV. Carbon Laser Facial (Black Doll)
Device: 1320 nm Nd:YAG + carbon powder
Goal: Carbon absorbs laser energy, causing explosion and cleaning pores, improving tone and texture.
| Reaction | Explanation | Energy Evaluation |
| Crisp, even popping sound | Proper energy and focus distance | Ideal endpoint |
| Mild warmth and redness | Normal epidermal heating | Safe |
| Brighter, smoother skin after treatment | Successful keratin removal | Effective |
⚠️ Abnormal: heavy popping sound or burning smell, gray/black crusts, or redness lasting >1 day suggest overexposure or close distance.
V. Comprehensive Comparison Table
| Procedure | Wavelength | Target Layer | Ideal Endpoint | Abnormal Signs |
| Eyebrow Removal | 532/1064 nm | Epidermis – Superficial Dermis | Whitening, mild redness, no bleeding | Bleeding, carbonization, purpura |
| Lip Lightening | 1064 nm | Mucosa – Superficial Dermis | Gray-white fog-like, mild redness | Bleeding, thick scab, swelling |
| Carbon Laser Facial | 1320 nm | Epidermal Stratum Corneum | Crisp popping, mild heat, redness | Burn smell, scab, persistent erythema |
Operators must master the characteristic endpoint reactions of each treatment, understand the clinical significance of energy control, and ensure both safety and efficacy.
