Principles of pigment lasers: selectively destroying melanin

💡 At a glance

· Pigment lasers use the principle of selective photothermolysis to destroy only melanin while preserving the surrounding skin.

· Three operating factors: ① a wavelength that melanin absorbs well ② a pulse shorter than the melanosome thermal relaxation time (about 250~1,000 nanoseconds) ③ sufficient energy (fluence).

· Short wavelengths (532nm) act on superficial epidermal pigment, while long wavelengths (1,064nm) act on deeper dermal pigment.

· Pico lasers have pulses about 100 times shorter than Q-switched (nanosecond) lasers, creating a stronger 'shattering' photomechanical effect and a lower risk of post-inflammatory hyperpigmentation.

A pigment laser (pigment laser, 色素レーザー, 色素激光, Q-switched·pico laser, laser toning) is a laser treatment that selectively destroys melanin pigment in the skin with light to fade spots, melasma, freckles, Ota nevus, tattoos, and more. Even among 'lasers,' the target pigment and depth can vary completely depending on the wavelength and pulse duration, and the key principle that determines this difference is selective photothermolysis.

What exactly is the principle of pigment lasers?

Melanin, which determines skin color, is contained in small sacs called melanosomes (cell organelles about 0.5~1µm in size). Pigment lasers use the property that this melanin absorbs light of a specific wavelength and heats up instantly. When light energy is concentrated in the melanosome, tiny vapor bubbles (cavitation) and shock waves are generated inside, and as a result, the pigment particles are broken into fine pieces and gradually removed by immune cells (macrophages).

The key to this process is "heating only melanin and not the surrounding normal tissue." The theory formalized this is selective photothermolysis, published by Anderson and Parrish in 1983, and it has become the scientific foundation of almost all pigment, tattoo, and hair removal lasers today.

Three conditions for selectively destroying only melanin

For selective photothermolysis to hold, three conditions must be met at the same time.

1) Wavelength — it must be light that melanin absorbs well. Melanin has a broad absorption spectrum spanning ultraviolet to near-infrared, and the shorter the wavelength, the higher the absorption. In a Q-switched Nd:YAG study, the threshold energy at which the skin turned white was about 0.20J/cm² at 532nm and about 1.0J/cm² at 1,064nm, showing that shorter wavelengths produced a response with much less energy.

2) Pulse duration — it must be shorter than the target’s thermal relaxation time. Thermal relaxation time (TRT) is the time it takes for a heated structure to cool by half, and it is shorter for smaller targets. The TRT of melanosomes is estimated to be about 250~1,000 nanoseconds, and if the pulse is shorter than this, melanin is destroyed instantly before heat can spread to the surrounding tissue. Q-switched lasers (nanoseconds) and pico lasers are devices designed to meet this condition.

3) Energy (fluence) — it must be sufficient to destroy the target. If it is too weak, there is no effect; if it is too strong, the risk of burns and pigmentation increases, so it is precisely adjusted according to the type of pigment and skin type.

Wavelength determines depth

The longer the wavelength of light, the deeper it penetrates the skin. Therefore, short wavelengths with high absorption, such as 532nm, are advantageous for freckles and age spots located in the epidermis, while long wavelengths that reach deeper, such as 1,064nm, are better for pigments located deep in the dermis, such as Ota nevus and tattoos. This is why the wavelength must be changed depending on the depth even for the same pigment.

Q-switched vs pico: the difference created by pulse duration

Q-switched (QS) lasers emit light in nanoseconds (10⁻⁹ seconds), while pico lasers emit light in picoseconds (10⁻¹² seconds), about 1,000 times shorter. In actual devices, pico pulses are about 100 times shorter than nanosecond pulses, which results in much greater instantaneous pressure (peak stress).

The shorter the pulse, the more the pigment is broken by 'impact' (photomechanical effect) rather than 'heat,' and reports suggest that this reduces thermal damage to surrounding tissue and the risk of post-inflammatory hyperpigmentation (PIH). Shimojo et al. (2024, Lasers in Surgery and Medicine) precisely measured the threshold energy required to destroy melanosomes with 532·730·755·1,064nm pico lasers and reported that the shorter the wavelength, the less energy was needed to fragment the pigment. However, pico is not always superior, and Q-switched lasers may be more appropriate depending on the type and depth of pigment and skin type.

Approach by pigment type

• Epidermal pigment (freckles·spots·age spots): The 532nm class with high absorption is effective, and improvement is usually seen in 1 to several sessions.
• Dermal pigment (Ota nevus, etc.): Treated over multiple sessions with 1,064nm·755nm classes that penetrate deeply.
• Melasma: Because melanin reacts sensitively to sunlight and hormones, strong energy can actually make it worse, so the 'laser toning (low-output Q-switched 1,064nm)' method of delivering multiple low-energy passes is standard. This is based on the concept of 'subcellular selective photothermolysis,' which stimulates melanosomes in fine detail at the cellular level.

Deore clinical principles

In our clinic, rather than trying to erase pigment aggressively no matter what, we first evaluate the type and depth of the pigment and the skin tone (Fitzpatrick type), then gradually adjust the wavelength and energy. In particular, because East Asian skin contains more melanin and has a relatively higher risk of post-treatment pigmentation when exposed to strong energy, Deore clinical practice uses conservative settings that 'start gently and increase while observing the response,' along with thorough sunscreen education.

Frequently asked questions

Q1. Will one pigment laser session remove all spots?

Superficial epidermal spots and freckles often fade noticeably in 1 to several sessions, but dermal pigment and melasma require treatment over multiple sessions. Results vary greatly depending on the depth and amount of pigment.

Q2. Are pigment lasers and laser toning the same?

Laser toning is one type of pigment laser. It is a technique that uses low-output Q-switched 1,064nm in multiple passes with a wide spot size, mainly for melasma and subtle pigment, and its purpose and settings differ from general pigment treatment that breaks clear spots with a strong single exposure.

Q3. I have darker skin. Won't pigmentation (hyperpigmentation) occur after a pigment laser?

The more melanin there is, the more laser energy is absorbed by the epidermis, increasing the risk of post-treatment hyperpigmentation (PIH). Therefore, lower-output, split treatments and thorough sun protection are especially important for darker skin, and a prior skin type assessment is essential.

Q4. I got a scab after a pigment laser. Can I pick it off?

Strong treatment of epidermal pigment may cause small scabs. Pulling them off forcefully can lead to hyperpigmentation or scarring, so leave them until they fall off naturally and maintain moisturizing and sun protection.

Q5. Is pigment laser effective for melasma?

It can be effective, but caution is needed. Because melasma can worsen with strong energy, a low-output toning approach is recommended, and results are more stable when combined with whitening agents and lifestyle care rather than used alone.

Closing

The core of pigment lasers is not 'how strongly you fire it,' but 'how precisely you selectively destroy only melanin.' Even with the same pigment laser, results and safety vary greatly depending on how wavelength, pulse, and energy are combined, so customized settings matched to the type of pigment and skin type are most important. Accurate diagnosis and settings should always be determined through consultation with a medical professional.

ℹ️ This content is intended to provide general medical information and does not replace individual medical care. Treatment results may vary depending on each person’s skin condition, and accurate diagnosis and consultation should be done with a specialist in skin aesthetics.