Ensuring optimal treatment outcomes while minimizing adverse reactions has always been a central challenge in medical aesthetics. Traditional high-fluence laser protocols are effective but frequently associated with complications such as post-inflammatory hyperpigmentation (PIH) and barrier disruption—especially in melanin-rich Asian skin types.
Low-Fluence, High-Spot-Size (LFHSS) laser technology offers a safer alternative by combining gentle thermal effects กับ precise pigment targeting. Today, this technique is widely applied in 1064 nm / 755 nm- nanosecond และ picosecond platforms.
This article provides a comprehensive scientific and clinical overview of LFHSS: its origin, standardized definition, indication-specific parameters, treatment precautions, and contraindications—offering physicians a structured and evidence-based protocol.
1. Origin and Standard Definition
1.1 Historical Background
LFHSS can be traced back to the mid-2000s, when Korean dermatologists first applied large spot sizes and low fluence กับ Q-switched Nd:YAG 1064 nm nanosecond lasers for melasma management—coining the term Laser Toning-
The approach quickly gained global popularity and later inspired technologies such as “Whitening Toning,” “Carbon Peeling,” and other low-fluence programs.
With device evolution, LFHSS expanded to 755 nm nanosecond and picosecond lasers, enabling more precise pigment-selective treatment and significantly reduced risk of complications.
1.2 Standard Definition of LFHSS
LFHSS must meet all of the following technical criteria:
| พารามิเตอร์ | Standard Requirement |
|---|---|
| ขนาดจุด | ≥ 6 mm |
| Fluence | ≤ 3 J/cm² |
| Treatment Endpoint | Mild warming or slight erythema |
Wavelength Characteristics
- 1,064 นาโนเมตร → deeper penetration; targets dermal pigment (melasma, Hori’s nevus, PIH)
- 755 nm → higher melanin absorption; ideal for epidermal pigment (freckles, epidermal melasma)
ระยะเวลาชีพจร
- Picosecond → photomechanical pigment fragmentation + skin rejuvenation
- Nanosecond → epidermal/dermal modulation and skin conditioning
2.1 Pigmentary Disorders
(1) Melasma – 1064 nm Nanosecond Laser as Standard of Care
Recommended Parameters
- Spot size: 6–8 mm
- Fluence: 1–3 J/cm²
- Frequency: 5–10 Hz
- Interval: every 2–4 weeks
- Total sessions: ≤ 15 sessions
(Exceeding 15 sessions increases risk of mottled hypopigmentation.)
Mechanism:
LFHSS applies “subcellular selective photothermolysis”—breaking melanosomes while preserving melanocyte viability, thereby reducing PIH and rebound pigmentation.
(2) Hori’s Nevus / Dermal Melanocytosis
First choice:
755 nm picosecond laser
→ stronger photomechanical fragmentation
→ lower risk of PIH
If using a 1064 nm nanosecond device:
- Spot size: 6–8 mm
- Fluence: 1–3 J/cm²
- Frequency: 5–10 Hz
- Interval: 2–4 weeks
2.2 Inflammatory & Degenerative Skin Conditions
(1) Rosacea & Steroid-Induced Dermatitis
Recommended (1064 nm nanosecond “toning mode”)
- Spot size: 6–8 mm
- Fluence: 0.3–1.5 J/cm²
- Interval: 4 weeks
Mechanisms:
- Modulates vascular reactivity
- Reduces inflammatory cytokines
- Accelerates barrier repair
- Improves flushing and sensitivity
(2) Skin Rejuvenation (755 nm Picosecond + MLA Technology)
Recommended Parameters
- Spot size: 6–8 mm
- Fluence: 0.5–1.0 J/cm²
- Frequency: 5–10 Hz
- Interval: every 4 weeks
ประโยชน์:
- Collagen neogenesis
- Texture and pore refinement
- Fine lines reduction
- การหยุดทำงานน้อยที่สุด
3. Treatment Precautions
3.1 Patch Test Protocol (Mandatory Step)
- Start with 1 J/cm², deliver 1–2 shots, observe for 5 minutes
- If purplish erythema or pain → decrease fluence by 0.2–0.5 J/cm²
- If minimal reaction → increase by 0.2–0.5 J/cm² (not exceeding 3 J/cm²-
- During full-face treatment, ensure the skin temperature stays below 40°C after 2–3 passes.
3.2 Preventing Excess Energy Accumulation
- Overlap rate: ≤ 10%
- Melasma: do not exceed 15 lifetime sessions
- Periocular & perioral areas: reduce fluence by 20%
- Always enable device cooling
(air cooling / contact cooling / cryogen depending on device)
4. Contraindications
4.1 High-Vascular-Density Lesions (Port-Wine Stain, Hemangioma)
1064/755 nm wavelengths have low hemoglobin absorption →
LFHSS fluence is insufficient to coagulate vessels →
May worsen vascular proliferation → Contraindicated
4.2 High-Density Tattoo Pigment
LFHSS fluence cannot reach the “instantaneous pigment explosion threshold” needed for tattoo removal.
- Leads to inadequate fragmentation
- Requires excessive sessions
- Increases inflammation and PIH
→ Use high-fluence Q-switched or picosecond protocols instead.
4.3 Hyperkeratotic Lesions (Seborrheic Keratosis, Warts)
LFHSS is non-ablative and relies mainly on photobiomodulation →
Cannot vaporize keratin →
May stimulate further hyperkeratosis → Contraindicated
บทสรุป
LFHSS technology, based on large spot size and low fluence, provides a safer, gentler laser strategy across multiple wavelengths and pulse modes. It offers significant benefits in:
- Pigmentary disorders
- Inflammatory skin conditions
- Skin rejuvenation
- Sensitive-skin management
However, clinicians should note:
- Clear clinical consensus currently exists only for melasma
- 15 sessions increases risk of mottled hypopigmentation
- Evidence for rosacea and rejuvenation requires more long-term RCTs
- Contraindications must be strictly followed
Future studies—especially multicenter randomized controlled trials—are essential to further define LFHSS treatment boundaries, optimize parameters, and elevate safety standards across medical aesthetic practice.
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