Lasers have been used in dermatology for over 40 years. With the proposal of the theory of selective photothermal action in 1984, short-pulse laser has been widely used in dermatology, and has achieved great results in pigmented skin diseases, vascular skin diseases, hair removal, superficial tumors, and wrinkle removal. The breakthrough has brought the gospel to the majority of patients. In this chapter, we will mainly introduce the commonly used dermatology laser therapy instruments and their indications in clinical practice. In fact, there are so many types of lasers used in dermatology that it is impossible to list them all because of space limitations.

• Continuous laser:

The energy of the laser is continuously output, and the selectivity of this type of laser to the therapeutic target is not strong, mainly including: carbon dioxide laser, argon ion laser, helium neon (He-e-Ne) laser, etc.

• Quasi-CW Laser:

The energy of this type of laser is output in the form of pulses, but the output pulse frequency is very high, and the biological effects and actual clinical effects on skin tissue are not significantly different from those of continuous lasers, so they are called quasi-continuous lasers. The two are basically equivalent and are sometimes grouped together in classification. Like CW lasers, quasi-CW lasers are not very selective for therapeutic targets. The main quasi-continuous lasers include: copper vapor laser, krypton laser, potassium titanium phosphate (KTP) laser, etc.

• Pulsed laser:

The energy of the laser is output in the form of short pulses, and the pulse width is very short, generally in the nanosecond (ns) and millisecond (ms) level. This type of laser is based on the theory of selective photothermal action, which is highly selective to the target without obvious damage to the surrounding normal tissue, thus achieving the ideal effect of non-invasive treatment. Representatives of pulsed lasers include: Q-switched alexandrite laser, Q-switched ruby laser, Q-switched Nd:YAG laser, pulsed dye laser, Q-switched erbium laser, ultrashort pulse carbon dioxide laser, Q-switched semiconductor laser, etc.

AG laser, is a solid-state laser, which can be used for disinfection and sterilization.

(1) Technical parameters: the wavelength is 308nm, and the single pulse energy is 50-3300mJ.
(2) Principle of action: It can promote melanin synthesis and melanocyte proliferation; and induce T cell apoptosis, which has an immunoregulatory effect.
(3) Indications: Clinically, it is mainly used for the treatment of vitiligo and psoriasis, with good curative effect. In addition, it can also be used for the treatment of skin diseases such as alopecia areata, lichen planus, and eczema.

(1) Technical parameters: The wavelength is 355nm, which is a solid-state laser; continuous pulsed Q-switched laser
(2) Application: At present, such lasers are widely used in flow cytometry.

(1) Technical parameters: wavelength 405nm, semiconductor laser; continuous laser
(2) Application: Mainly used in laser fluorescence induction.

(1) Argon ion laser, CW laser

(2) Application: Mainly used in laser fluorescence induction and surgical cutting and coagulation.

(1) Technical parameters: The wavelength is 532nm, which is obtained by frequency doubling of a neodymium-doped yttrium-aluminum garnet laser (wavelength 1064nm) by a special crystal. The pulse width is generally 4-10ns in the Q-switched mode, and the pulse width in the long-pulse-width mode is generally 4-10ns. The width is variable from 2 to 50ms.
(2) Principle of action: Based on the principle of selective photothermal action, both oxyhemoglobin and melanin have a good absorption effect on this wavelength.
(3) Indications: Clinically, it is mainly used for the treatment of superficial hyperpigmented skin diseases, such as freckles and café-au-lait spots. Long pulse width mode can treat vascular proliferative skin diseases such as port-wine stains, telangiectasia, rosacea (telangiectasia type), etc.

(1) Technical parameters: The system has two wavelengths: 585nm and 595nm. The pulse width of the former is 300-450μs, and the pulse width of the latter is adjustable at 0.4-40ms.
(2) Treatment principle: based on the principle of selective photothermal action. Both wavelengths are well absorbed by oxyhemoglobin and penetrate into the dermis. After the laser energy is absorbed by oxyhemoglobin, the hemoglobin and the blood vessel wall are coagulated by the thermal effect, thereby sealing the blood vessel. Relatively speaking, oxyhemoglobin absorbs more strongly at wavelengths of 585 nm, while wavelengths at 595 nm penetrate deeper.
(3) Indications: Clinically, it is mainly used for the treatment of vascular proliferative skin diseases, such as port-wine stains, telangiectasia, angiokeratoma, rosacea (capillary damage type), spider nevus, and can also be used for the treatment of Flat warts, plantar warts, hypertrophic scars, etc. There is generally no scarring after this laser.

(1) Technical parameters: the wavelength is 632.8nm, and the output power is generally 10-40mW.
(2) Principle of action: He-Ne laser has the following functions: improving skin microcirculation, strengthening metabolism, and promoting the recovery of tissue structure and function; accelerating absorption, reducing inflammatory reactions such as congestion and edema; regulating immune function; accelerating pain Absorption of chemical mediators, play an analgesic effect.
(3) Indications: skin ulcers, alopecia areata, herpes zoster and after-effects pain, folliculitis, etc.
(4) Contraindications: photosensitivity diseases, malignant tumors, acute infections, etc.

(1) Technical parameters: wavelength 635nm, semiconductor laser; continuous laser.
(2) Application: mainly involved in light adjustment.

(1) Technical parameters: wavelength 650nm, semiconductor laser; continuous laser.
(2) Application: mainly involved in light adjustment.

(1) Technical parameters: 694nm wavelength, ruby laser; pulsed Q-switched laser.
(2) Application: It is mainly used in the treatment of various pigmented diseases.

(1) Technical parameters: the wavelength is 755nm, the pulse width of the alexandrite laser is 50-100ns in the Q-switch mode, and the pulse width can reach the millisecond level in the long pulse width mode.
(2) Principle of action: The laser is based on the principle of selective photothermal action, and its target is mature melanosomes, thereby destroying the melanocytes where these melanosomes are located. Because the pulse width is shorter than the thermal relaxation time of the melanosome, there is no obvious damage to the surrounding normal tissue. In addition, the alexandrite laser can penetrate into the dermis, so it can treat dermal hyperpigmented skin diseases.
(3) Indications: Under the Q-switching mode, the indications are mainly for various epidermal and dermal hyperpigmented skin diseases, the former including freckles, café-au-lait spots, seborrheic keratosis, freckled nevus, Becker nevus, etc., the latter Including nevus of Ota, acquired nevus-like spots of Ota, tattoos, foreign body tattoos, etc. Alexandrite laser has the ideal effect of non-invasive treatment, and there is basically no scarring after surgery. In the long pulse width mode, the alexandrite laser is mainly used for hair removal.

(1) Technical parameters: the wavelength is 808nm, and the pulse width is generally adjustable from 10 to 300ms.
(2) Principle of action: This wavelength can be absorbed by the mature melanin in the hair follicle, thereby destroying the hair follicle through thermal damage. Generally, it has a stronger effect on hair follicles in the growing period. Longer pulse widths are more beneficial for the treatment of dark-skinned people.
(3) Indications: It is mainly used for hair removal in clinic, with good curative effect and lasting effect. In addition, it can also be used for the treatment of hairy moles, pseudofolliculitis and some hyperpigmented skin diseases.

(1) Technical parameters: wavelength 810nm, semiconductor laser; continuous pulse laser.
(2) Application: mainly involved in light adjustment, hair removal.

(1) Technical parameters: wavelength 830nm, semiconductor laser.
(2) Application: used for skin laser confocal microscope.

(1) Technical parameters: wavelength 970nm, semiconductor laser.
(2) Application: for surgery.

Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser continuous
(1) Technical parameters: the wavelength is 1064nm, and the power is generally 10-80W.
(2) Action principle: The output wavelength of Nd:YAG laser is located in the near-infrared region, which mainly produces thermal effect in skin tissue, resulting in gasification, carbonization and coagulation of skin tissue. This wavelength penetrates deeply in the skin tissue, has a strong coagulation effect, and has a large thermal damage range.
(3) Indications: Nd:YAG laser is mainly used for the treatment of vascular proliferative lesions, such as cavernous hemangioma, lymphangioma, angiokeratoma, pyogenic granuloma, hemangioendothelioma, Kimura disease, etc. Treatment of common warts and plantar warts.

Q-Switched Pulsed Neodymium-Doped Yttrium Aluminum Garnet Laser
(1) Technical parameters: the wavelength is 1064nm, the pulse width is 5-40ns in the Q-switch mode, and the pulse width can reach the millisecond level in the long pulse width mode.
(2) Principle of action: It is also based on the principle of selective photothermal action. The long wavelength and deep penetration of the laser are its characteristics.
(3) Indications: It mainly treats various dermal hyperpigmented skin diseases, such as Ota nevus, acquired Ota nevus-like spots, tattoos, etc., basically without scarring. The long pulse width mode is mainly used for the treatment of vascular proliferative skin diseases such as strawberry hemangioma, port-wrinkle, telangiectasia, etc. It can also be used for hair removal, wrinkle removal and skin tightening.

(1) Technical parameters: The wavelength is 1440nm, which is a solid-state laser; a pulsed laser.
(2) Application: used for the treatment of scars and wrinkles.

(1) Technical parameters: The wavelength is 1320nm, which is a solid-state laser; a pulsed laser.
(2) Application: used for the treatment of scars and wrinkles.

(1) Technical parameters: The laser is a focal skin grinding system with a wavelength of 1550 nm, a pulse energy of 4.5 to 40 J, and a diameter of 50 to 200 μm. , so it is also called “dot-matrix laser” or “pixel laser”.
(2) Action principle: The laser action is based on the principle of focal photothermal action, and can punch micro-holes with a diameter of only 50-200 μm on the skin, with normal skin between the holes. These micropores damage part of the dermal tissue and stimulate the skin repair mechanism to make the dermis produce more new collagen and reorganize, which has the effect of removing wrinkles and rejuvenating the skin. Because the pores are very small and surrounded by normal skin, they heal quickly and generally do not leave scars.
(3) Indications: Mainly used for photoaging, wrinkle rejuvenation, depressed scar, and sometimes melasma.
(4) Contraindications: patients with scar constitution, those who are prone to pigmentation or abnormalities, mentally ill patients, patients with active vitiligo and psoriasis, and those with active infection in the treatment area are contraindicated.

(1) Technical parameters: wavelength 1927nm, thulium-doped fiber laser, solid pulse laser.
(2) Application: for the treatment of urology and skin surgery.

(1) Technical parameters: The wavelength is 2000nm, which is a semiconductor laser and a pulsed laser.
(2) Application: for the treatment of urology and skin surgery.

(1) Technical parameters: wavelength 2100nm, holmium-doped continuous fiber laser, solid pulse laser.
(2) Application: for the treatment of urology and skin surgery.

(1) Technical parameters: wavelength 2790nm, solid-state laser; pulse, lattice laser.
(2) Application: used for the treatment of scars and wrinkles.

(1) Technical parameters: the wavelength is 2940nm, and the pulse width is generally 300μs.
(2) Treatment principle: based on the principle of selective photothermal action. The wavelength of the laser is located near the absorption peak of water, so the water molecules in the tissue are used as the target to ablate and vaporize the skin tissue, and its pulse width is shorter than the thermal relaxation time of the skin tissue, which greatly reduces the normal operation around the target. Thermal damage to the tissue, allowing more precise control of the depth of treatment.
(3) Indications: The indications for lasers mainly include 3 types:

① Benign superficial skin tumors and neoplasms (such as syringoma, pilosepithelioma, eyelid xanthoma, pigmented nevus, seborrheic keratosis, etc. );
② atrophic or depressed scars;
③ wrinkle removal. The bait laser has better clinical effects and fewer adverse reactions.

(1) Technical parameters: The wavelength is 10 600nm, and the power is generally 10-50W.
(2) Principle of action: The wavelength of carbon dioxide laser is located in the mid-infrared region, and the main target is water molecules, which can lead to a significant increase in the temperature of skin tissue, resulting in biological effects such as coagulation, carbonization, and gasification. and so on. Fractional laser can directly reach the deep dermis of the skin, stimulate the dermal tissue at the damaged site to repair the mechanism, and make the dermis produce more collagen and rearrange it to rejuvenate the skin. Fractional laser can punch micro-holes with a diameter of 120-1200μm on the skin, and the hole spacing is 500μm. During the treatment process, the energy is randomly scanned and released, and normal skin tissue is left between each spot, thereby starting the body’s natural healing mechanism and promoting collagen. protein regeneration.
(3) Indications: Clinically, carbon dioxide laser is mainly used to remove benign growths and tumors on superficial skin, including common warts, condyloma acuminatum, seborrheic keratosis, pigmented nevus, skin tags, skin angle, keratosis Acanthomas, pyogenic granulomas, etc., are sometimes used in the treatment of tumors such as Bowen’s disease, basal cell carcinoma, and squamous cell carcinoma. After the carbon dioxide laser has been expanded, it can be irradiated as a low-power laser for the treatment of skin ulcers, pruritus, cold erythema multiforme and frostbite. Fractional laser is mainly suitable for treating uneven skin tone, rough skin, sagging, improving scars, removing superficial pigmentation, increasing skin elasticity and gloss.

In the visible to near-infrared region, melanin is a natural target in hair follicles. Lasers or light sources with wavelengths in the red and near-infrared regions can be selectively absorbed by melanin and penetrate deep into the dermis. In this way, light with a wavelength of 600-1100 nm is entirely possible to selectively heat the deep hair shaft, hair follicle and pigment-rich matrix. Photothermal damage is based on the principle of selective photothermal action. According to this principle, when the wavelength of light can be better absorbed by the target material, its action time is equal to or less than the thermal relaxation time of the target material, and the dose is sufficient, it will cause selective thermal damage to the pigment target. The current laser equipment for hair removal is based on this principle, but there is no melanin in the white hair as a target tissue, and it cannot absorb the laser of the corresponding wavelength, so the effect of hair removal cannot be achieved. Therefore, there is no laser for white hair removal in laser treatment so far.

Fractional laser photothermal acts locally and acts on a small part of the skin. Its basis is to divide a continuous laser spot into many evenly distributed lattice focusing. Lasers with strong water absorption, such as pulsed semiconductor lasers, CO2 lasers or bait lasers, etc., when the diameter of the laser beam is adjusted to several hundreds of microns, under a certain energy density, the laser beam can penetrate through the epidermis and enter the dermis. This type of laser has better absorption of water, so the tissue in the part where the laser passes will generate heat due to the absorption of laser energy. The laser penetrates the skin to form a real aperture, whether thermal denaturation or real aperture formation, this damage will initiate the body’s programmed wound healing process. If these beams are arranged in a lattice, then this point The burst thermal stimulation evenly initiates the skin repair process, eventually leading to full-thickness skin remodeling and reconstruction, including the epidermis and dermis, for therapeutic purposes. Therefore, it has a certain effect on the skin structure with high water content, and has a good effect on telangiectasia, neurofibromatosis, xanthoma, acne pits, skin tightening, etc.

Ota nevus, blue-green nevus, melanocytic nevus, congenital generalized melanocytic nevus, blue nevus, pigmented hairy epidermal nevus, pigment incontinence, congenital pigmented nevus, familial progressive hyperpigmentation, hereditary Symmetrical pigment incontinence, hereditary generalized dyschromia.

The sebaceous gland is a lipid-producing organ and is a vesicular gland composed of acini and short ducts. The acinus has no glandular cavity, and the outer layer is flat or cuboidal cells surrounded by basement membrane bands and connective tissue. After the gland cells rupture, the lipid droplets are released and discharged through the duct. The sebaceous glands are mainly composed of lipids and can absorb laser beams with a wavelength of 1270 nm, but no related lasers have been developed so far.