Which technology suits which treatment?

Energy in the right place in the skin

Energy-based devices (EBDs), such as lasers, deliver energy into the skin, either as light or as electrical current. Where that energy is absorbed, heat is usually generated. How the tissue responds to that heat determines the clinical result. In a vascular lesion, the blood coagulates and the body then clears the vessel. In skin rejuvenation, the skin produces new collagen around the heated zones.

So technologies differ mainly in where the energy ends up: in which structure, at what depth and over what length of time. That gives us three groups.

By treatment

Below is a brief summary of the technologies used for each indication. Why they are used, and which devices go with them, is explained on each indication page.

• Hair removal: alexandrite (755 nm) for light to medium skin (Fitzpatrick I–IV), long-pulse Nd:YAG (1064 nm) for dark skin, because the melanin in the epidermis absorbs that wavelength less ^[1]. For skin type IV, a borderline case, both are used. Diode lasers around 800–810 nm are also widely used; their wavelength lies between those of alexandrite and Nd:YAG.
• Vascular lesions: vascular lasers (532 and 577 nm in our range; the pulsed dye laser at around 585–595 nm is also widely used) and IPL for fine, superficial vessels and diffuse redness, long-pulse Nd:YAG for larger and deeper vessels.
• Pigmentation: Q-switched and picosecond lasers for sharply defined pigmented spots, IPL for superficial, diffuse pigmentation on light skin.
• Melasma: low-energy Q-switched Nd:YAG and picosecond lasers, alongside topical treatment.
• Tattoo removal and permanent makeup removal: picosecond and Q-switched lasers, with a wavelength matched to the colour of the ink.
• Benign skin lesions: ablative lasers (CO₂, erbium); for pigmented lesions such as seborrhoeic keratoses, also long-pulse alexandrite.
• (Acne) scars and stretch marks: fractional lasers, ablative (CO₂, erbium) or non-ablative (1540–1550 nm, Nd:YAP), RF microneedling and picosecond lasers.
• Wrinkles: fractional lasers, ablative (CO₂, erbium) or non-ablative (1540–1550 nm, thulium), and RF microneedling.
• Skin rejuvenation and skin quality improvement: fractional lasers, RF microneedling, IPL and picosecond lasers.
• Skin tightening: monopolar RF and RF microneedling.
• Acne: LED and IPL for active acne, as an adjunct to drug treatment.

The wavelength determines where the light ends up

Of the three groups on the map, the first two work with light. Whether a laser targets water or a chromophore depends on its wavelength: every substance in the skin absorbs some wavelengths strongly and others barely at all ^[2][3].

The haemoglobin absorption peaks that lasers make use of lie in green and yellow light, at around 542 and 577 nm. Below 600 nm, oxygenated and deoxygenated blood absorb about equally; between roughly 600 and 800 nm, deoxygenated blood absorbs markedly more ^[3]. Melanin absorbs light over a broad range, and more strongly the shorter the wavelength. That is why you often see 1064 nm used for darker skin types: melanin absorbs less there, so the epidermis takes up less heat and the light penetrates deeper ^[1].

From about 1300 nm, water takes over. At 1340 and 1540–1550 nm that absorption is still modest: the light reaches deeper and heats the tissue without vaporising it. Around 1927 nm it is much stronger, and around 2940 nm, the wavelength of the Er:YAG laser, it peaks. At 10,600 nm, the wavelength of the CO₂ laser, water still absorbs strongly, but about fifteen times less than at 2940 nm ^[2].

What determines the effect of a pulse?

The wavelength determines where the light is absorbed. What the tissue does next depends on how the energy is delivered.

Pulse duration

Every structure has a thermal relaxation time: the time it takes to lose about half of its heat. The smaller the structure, the shorter that time. If the pulse is shorter than the thermal relaxation time, the heat stays in the target ^[4]. In hair removal, the actual target, the stem cells around the follicle, sits just next to the pigment. Here the pulse can deliberately be longer, so that the heat reaches those cells ^[5].

Fluence, spot size and cooling

Fluence is the energy per unit area. A larger spot reaches deeper, because less light is lost to scattering at the edge of the beam. Cooling the skin surface protects the epidermis, especially in dark skin. If the next pulse lands on the same spot before the tissue has cooled, heat builds up; in dark skin, that increases the risk of pigmentary changes ^[1].

Ablative or non-ablative

Lasers that target water are used mainly for skin rejuvenation, scars, wrinkles and uneven texture. They usually work fractionally: the laser treats a grid of microscopic zones and leaves the skin in between intact. From these untreated bridges, the skin recovers much faster than when the entire surface has been treated ^[6].

An ablative laser vaporises the tissue in those zones. CO₂ and erbium light is absorbed in the top few micrometres; even so, the columns reach into the dermis, because the energy that follows keeps working in the opening that has formed. A rim of coagulated tissue remains around each opening. Per treatment, the effect is greater and the downtime longer than with a non-ablative laser.

A non-ablative laser coagulates columns of tissue through the epidermis into the dermis, but leaves the stratum corneum intact, so no open wound forms. Non-ablative treatments usually take more sessions, with less downtime per session. Thulium (1927 nm) works mainly superficially, in the epidermis and upper dermis, and is therefore also used for pigment. At 1540–1550 nm and 1340 nm, the columns reach deeper.

The difference between the two ablative lasers, CO₂ and erbium, lies mainly in the heat. Water absorbs CO₂ light less strongly than erbium light ^[2]. As a result, more heat spreads around each opening with CO₂; erbium vaporises tissue with little thermal damage around it ^[7]. What that means for results and downtime, and what comparative studies show, is covered on the erbium page.

Selective photothermolysis

The second group targets a single chromophore. In selective photothermolysis, you heat that chromophore while the surrounding tissue is spared ^[4]. To do so, you choose a wavelength absorbed mainly by that chromophore, and a pulse duration matched to the size of the structure, so that the heat stays in the target. The lesion itself also matters: a larger or deeper vessel calls for a longer wavelength and a longer pulse than a fine, superficial one.

With pigment and tattoo ink, the targets are so small that they cool within nanoseconds to a microsecond. Q-switched lasers, with nanosecond pulses, heat the particles so quickly that they break apart; besides heat, a mechanical effect also plays a part. Picosecond lasers deliver even shorter pulses, with a stronger mechanical (photoacoustic) effect and less heat ^[8]. According to a systematic review, they sometimes reach a comparable result in fewer sessions ^[8].

LED also works through chromophores, but without heat. Absorbers of the light include cytochrome c oxidase in the mitochondria and porphyrins ^[9]; red and near-infrared light act mainly through the mitochondria, blue light through porphyrins. LED has been studied most in acne, herpes simplex and zoster, and wound healing, including after a laser or IPL treatment ^[9]. In aesthetic practice, LED is used mainly in a supporting role, for example to aid recovery after another treatment.

Radiofrequency

Because radiofrequency does not need a chromophore, skin colour plays a much smaller role than with light. In dark skin, the risk of pigmentary changes is therefore lower, but not zero: blistering and hyperpigmentation have also been reported after RF, attributed to insufficient contact between the treatment tip and the skin ^[1].

Monopolar RF heats the deeper dermis and the fibrous septa in the subcutaneous fat over a large area. It is used mainly to tighten lax skin, for example along the jawline and on the neck.

In RF microneedling, needles, often insulated except at the tip, deliver the energy in small zones at a chosen depth in the dermis. This technique is used for scars, texture and laxity.

Our devices by technology

Some devices combine several technologies in one platform. You will find them under each technology they offer.

Target: water

• CO₂, ablative: eCO2 3D
• Erbium, ablative: DualMode (Er:YAG, 2940 nm), UltraClear (erbium fibre laser, 2910 nm)
• 1540–1550 nm, non-ablative: Mosaic 3D (Er:glass), FlexSys (diode)
• Thulium (1927 nm), non-ablative: LaseMD Ultra
• Nd:YAP (1340 nm), non-ablative: ProDeep

Target: a chromophore

• Vascular lasers, long pulse: DermaV (532 nm), FlexSys (532 and 577 nm)
• Nd:YAG (1064 nm), long pulse: Clarity II, Elite iQ, DermaV, LongPulse, ZYE YAG
• Nd:YAG, Q-switched and pico: Hollywood Spectra (Q-switched), PicoPlus and handPICO (pico)
• Alexandrite (755 nm), long pulse: Clarity II, Elite iQ, ZYE ALX
• Alexandrite (755 nm), pico: PicoSure Pro, with optional handpieces for 532 and 1064 nm
• IPL: IPL SQ, ReClear IPL
• LED: Healite II

No chromophore

• RF microneedling (bipolar): Genius
• Monopolar RF: XERF

Etherea MX is a platform for interchangeable handpieces (including LongPulse, handPICO, ProDeep, DualMode and IPL SQ) and is therefore listed under those handpieces. The ZYE platforms can also be expanded with those handpieces.