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Laser hair removal: mechanism of action, methodology, indications and contraindications
Medical expert of the article
Last reviewed: 04.07.2025
In the early 1990s, a revolution occurred in the field of hair removal, which is associated with the use of the first lasers.
Laser hair removal is a method of hair removal using a laser beam. The laser hair removal technique is based on the thermal effect that is created when light is absorbed by hair melanin. Laser radiation absorbed by hair melanin causes heating of the hair shaft, which heats up the adjacent follicular epithelium. The following lasers provide the most suitable radiation for hair removal: ruby, alexandrite, neodymium and diode. These lasers differ in the wavelength of the emitted light, as well as in the energy of the radiation and the duration of the pulses. Depending on the laser parameters, damage to the follicle can be photomechanical (in the case of a neodymium laser, when the main destructive factor is the rapid expansion of tissue when heated, or photothermal, when coagulation, charring (carbonization) or evaporation (vaporization) occurs.
Laser hair removal devices
The ruby laser generates red radiation with a wavelength of 694 nm - the maximum absorption of melanin. Hemoglobin absorbs weakly at this wavelength. The long-pulse ruby laser produces light pulses with a duration of about 3 ms, providing an energy flow of up to 40-60 J/cm 2. There is information on the use of a ruby laser for hair removal with a pulse duration of 0.5 ms (energy flow up to 20 J/cm 2 ). The pulse repetition rate of a ruby laser is usually about 1 Hz (one pulse per second), i.e. it is a relatively slow-acting laser.
Since the target for this type of laser is exclusively melanin, this type of hair removal is not applicable to tanned skin or light hair. The effectiveness of hair removal increases with skin types I and II according to Fitzpatrick in combination with dark hair.
The alexandrite laser generates radiation with a wavelength of 725 nm, i.e. also in the area of minimal absorption by hemoglobin and strong absorption by melanin. The pulse duration is 2, 5, 10 and 20 ms. Alexandrite is a faster laser compared to ruby, since the pulse repetition frequency is several times higher - about 5 Hz. The energy flow to the tissue is 10 J/cm2 per pulse in a laser pattern with a diameter of up to 10 mm. The restrictions on skin types and hair color for the alexandrite laser are the same as for the ruby laser.
The diode laser generates invisible light at a wavelength of 800 nm in the near infrared spectrum, i.e. also in the region of strong absorption by melanin. The pulse duration is from 5 to 30 ms, the frequency is 1 Hz, the energy flow to the tissue is 10-40 J/cm2 in a laser pattern with a diameter of 9 mm. The diode laser, like the ruby laser, cannot provide effective epilation of light and red hair, as well as hair on tanned skin.
Neodymium laser, or yttrium aluminum garnet laser, is widely used in medicine for tattoo removal. Laser radiation is generated by transitions of neodymium ions (Nd3+), which are built into yttrium aluminum garnet crystals (yttrium-aluminium garnet - YAG). Therefore, such a laser is often called "Nd:YAG laser". Nd:YAG laser emits in the near infrared range (1064 nm). This radiation is minimally absorbed in the upper layers of the skin and penetrates into the deep layers. The pulse duration is about 100 ns, i.e. much shorter than other types of laser.
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Photoepilation
In recent years, an alternative method of epilation has emerged, photoepilation. The method is based on the principle of selective photothermolysis. According to this principle, hair melanin absorbs light energy, which is then transformed into heat, which ultimately leads to the destruction of the hair follicle. Photoepilation uses a broadband light source, or a non-monochromatic light source. Intense light pulses are generated - from 400 to 1200 nm, covering the visible and near infrared wavelength ranges, i.e. in the area of strong absorption by melanin. Unlike lasers, the light pattern on the skin is a rectangle with an area of 4.5 to 10 cm 2, depending on the manufacturer. For example, "SPA TOUCH" by "Radiansi" uses patented LHE (Light Heat Energy) technology, which combines light and heat. About 85% of coagulation is performed by heat, and the remaining 15% by light. In order to penetrate the follicle and coagulate the hair bulb, the following 3 parameters are optimized in the SPA TOUCH: wavelength - 400-1200 nm, spot size - 55x22 mm and pulse duration - 35 ms. The SPA TOUCH device has the largest working area compared to other devices on the market. This allows the procedure to be performed on large areas, so, for example, the time spent on treating two shins is only 40-60 minutes. For comparison, the approximate time required for electrolysis is 4 to 6 hours for treating one shin, and laser hair removal - 1 to 2 hours for treating both shins.
The unconditional advantages of photoepilation are minor pain, non-invasiveness of the technique and the ability to affect a group of follicles at once. After the procedure, hair falls out within 10-14 days. Photoepilation can remove even the lightest hair. Red and gray hairs practically do not react to photo exposure. Therefore, such hair is removed using electrolysis. The frequency of procedures depends on many factors: the epilated area, hair growth rate, age, etc. Ingrown hairs are an indication for photoepilation not only in women, but also in men. After the first treatment, the number of folliculitis decreases by 60-70%.
Contraindications for laser or photoepilation procedures
Absolute contraindications include: tanning (procedures cannot be performed within 28-35 days after the last insolation), pregnancy, mental illnesses (in particular epilepsy), severe somatic diseases in the decompensation stage, herpes infection in the acute stage, open skin lesions, tumors, taking phototoxic drugs (systemic retinoids, tetracycline antibiotics, etc.).
Relative contraindications include: age under 18, hirsutism and hypertrichosis, tendency to keloids and hyperpigmentation, photodermatoses.
When performing laser or photoepilation, you may encounter side effects such as erythema and swelling of the skin at the site of the procedure, pigmentation disorders (hyper- and hypo-), and transient angiectasias.
Very often, it is necessary to use a combination of several epilations on one patient. After several laser or photoepilation procedures, a change in the structure and color of the hair is observed. Therefore, clients who want to continue hair removal are subject to electrolysis. After the procedure, the doctor should explain the features of caring for the treated area. When performing facial epilation, it is necessary to use a cream with a sun protection factor to avoid the development of hyperpigmentation. Between procedures, hair can only be shaved or trimmed, but in no case plucked or waxed.