Medical Lasers: Evolution and Clinical Applications of the GentleMax Pro System

Medical lasers have continued to evolve since Theodore Maiman introduced the first ruby laser in 1960. Beyond tissue coagulation and ablation, the most significant contribution to the understanding of tissue interaction occurred when Rox Anderson and John Parrish, in collaboration with Candela founder Horace Furumoto, published their research on selective photothermolysis in the journal Science in 1983.

The theory stated that lasers could target selective chromophores in tissues when laser wavelength, pulse duration, and the thermal relaxation time (TRT) of the target (which depends on its size and parameters) are taken into account. The ultimate goal of laser therapy is to affect the target in a specific desired manner while sparing the surrounding adjacent tissues. Desired effects of laser interaction with tissue may include denaturation, coagulation, apoptosis, and necrosis.

Since Maiman, numerous advancements have been made in laser technology, including the introduction of new wavelengths, increased fluences (energy densities), longer and shorter pulse durations, and the evolution of larger spot sizes. One example of this evolution is the GentleMax Pro laser, developed and manufactured by Candela Corporation.

Absorption Spectrum of 755 nm and 1064 nm Wavelengths

This paper discusses the wide range of applications for the GentleMax Pro, a dual-wavelength platform emitting laser energy at 755 nm (Alexandrite laser) and 1064 nm (Nd:YAG laser). Both wavelengths have significant absorption by skin chromophores; the 1064 nm wavelength is less sensitive to melanin but more sensitive to oxyhemoglobin compared to the 755 nm wavelength.

These wavelengths are well-studied for the removal of unwanted hair. They are also used to treat both vascular and pigmented pathologies. Additionally, the Nd:YAG laser is used for rejuvenation of aging skin, the treatment of hyperhidrosis, and onychomycosis. Melanin is the primary target for hair removal and pigmented lesions, while hemoglobin is the primary target for vascular applications.

The GentleMax Pro includes the Dynamic Cooling Device™ (DCD™), which sprays cryogen with adjustable duration before and after the laser pulse. The DCD protects the epidermis and reduces the risk of scarring and pigmentary changes, such as post-inflammatory hyperpigmentation (PIH).

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Laser Hair Removal

Hair removal has been desired for thousands of years, dating back at least to the Egyptians. In the 1800s, the razor and galvanic electrotherapy were introduced. Lasers were first described as a method for hair removal in 1963 by Leon Goldman, but the method did not reach commercial use until the 1990s.

To understand how lasers are used for hair removal, we must first discuss the anatomy and biology of the hair follicle and the hair growth cycle. Important structures include the dermal papilla, hair shaft, blood vessels, and the bulge area. Cells in the dermal papilla and bulge zones can produce hair; thus, to destroy the hair, both zones must be damaged. The theory of selective photothermolysis suggests that laser radiation at wavelengths from 690 nm to 1064 nm is predominantly absorbed by the pigment in the hair shaft and pigmented cells in the dermal papilla, leading to the destruction of the hair. Longer millisecond pulses allow the pigment in the hair shaft and papilla to dissipate heat such that the laser energy can destroy the desired target—the hair follicle.

Understanding the hair growth cycle is also crucial. The four cycles of hair growth are anagen, catagen, telogen, and exogen.

• Anagen is the active growth phase. Melanin synthesis and hair shaft growth begin here; by the end of this phase, the follicle contains the maximum amount of melanin and reaches its deepest point in the skin.
• Catagen is the regression phase, where growth and melanin production cease.
• Telogen is the resting phase, where the hair loses its connection to the dermal papilla.
• Exogen is when the hair eventually falls out.

Hair is most susceptible to laser energy from the beginning to the middle of the anagen phase, when the follicle has formed sufficient melanin but before the hair has penetrated deep into the dermis.

Wavelength Selection

Wavelength selection is based on skin type. Optimizing the contrast between epidermal pigment and the pigment in the hair shaft/papilla is critical. While early-generation lasers were generally contraindicated for Fitzpatrick skin types IV–VI, advancements over the last decade have led to devices that can be safely used on ethnic skin.

Longer wavelengths, such as the 1064 nm Nd:YAG, are less absorbed by epidermal melanin and penetrate deeper into the dermis, making them ideal for dark skin types. Lighter skin types with dark, coarse hair or finer brown hair can be effectively treated with the 755 nm Alexandrite laser, which has higher melanin absorption.

Pulse Duration

The pulse duration must be long enough to allow heat to dissipate from the epidermal melanin, but short enough to maintain an adequate temperature in the hair follicle for its destruction. The TRT for the epidermis is approximately 10 ms, while for the hair bulb, it is 20–40 ms. Therefore, when treating thick, coarse hair or dark skin, longer pulses (20–40 ms) are recommended.

Spot Size and Repetition Rate

A larger spot size allows the laser light to penetrate deeper into the skin. Spot size, combined with the repetition rate, determines the speed of the procedure; larger spot sizes and higher frequencies allow for faster treatment of large areas.

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Treatment of Vascular Pathologies

Historically, the argon laser was the first used for selective vascular treatment (488 nm and 514 nm). However, because it emitted a continuous beam, it caused non-specific thermal damage and scarring. This led to the development of Pulsed Dye Lasers (PDL).

The evolution continued with the Vbeam Perfecta (595 nm), which introduced “macro-pulses” consisting of up to 8 sub-pulses to provide effective yet gentle treatment. The GentleMax Pro (755 nm and 1064 nm) can also treat vascular pathologies.

• 755 nm: Higher hemoglobin absorption than 1064 nm; effective for thick Port-Wine Stains.
• 1064 nm: Deep penetration (4–6 mm); the “gold standard” for leg veins. Its low melanin absorption makes it safer for darker skin types (Fitzpatrick IV–VI).

Recommended Parameters:

• Resistant Port-Wine Stains: 755 nm, 8 mm spot, 3–5 ms pulse, 30–45 J/cm², DCD 50/30.
• Leg Veins: For blue veins (1–1.5 mm): 1064 nm, 3 mm spot, 30 ms pulse, 130–180 J/cm², DCD 50/30.
• Rosacea/Facial Telangiectasia: For diffuse redness, a “painting” technique is used: 1064 nm, 8 mm spot, 0.3 ms pulse, 8 J/cm², 10 Hz, DCD OFF.

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Treatment of Pigmented Pathologies

The 755 nm Alexandrite laser is highly effective for epidermal lesions such as lentigines and Cafe au Lait spots.

• Parameters: 8 mm spot, 3 ms pulse, 24 J/cm², DCD OFF. Most lesions respond after a single treatment.

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Treatment of Aging Skin

For non-ablative rejuvenation, the Nd:YAG laser is used to treat fine lines and wrinkles.

• Technique 1: 18 mm spot, 18 J/cm², 50 ms pulse, DCD OFF. The skin should be heated to 40–45°C.
• Technique 2 (“Painting”): 8 mm spot, 0.3 ms pulse, 8 J/cm², 10 Hz, DCD OFF.

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Treatment of Onychomycosis (Nail Fungus)

The 1064 nm Nd:YAG laser can penetrate the nail plate to temporarily increase nail clarity. This is an excellent alternative for elderly or immunocompromised patients who cannot take oral antifungals (like Terbinafine) due to liver or kidney concerns.

• Parameters: 0.3 ms pulse, 2–3 Hz, 14–18 J/cm², DCD OFF.

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Treatment of Hyperhidrosis

Selective deep heating of melanin in the hair follicle bulb with 1064 nm light can damage the adjacent eccrine sweat glands, leading to a noticeable reduction in underarm sweating.

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Conclusion

The GentleMax Pro, with its combination of 755 nm and 1064 nm wavelengths, serves as the “gold standard” for hair removal across all skin types. Its versatility allows for the safe and effective treatment of vascular conditions, benign pigmented lesions, onychomycosis, and skin aging, making it one of the most comprehensive platforms in aesthetic medicine.