Laser hair removal is one of the most popular cosmetic procedures. Speed of hair removal, minor pain and permanent effect make laser hair removal a much-in-demand treatment. That is why almost every laser manufacturer tries to offer their devices for this treatment.

Laser and photo hair removal is based on the effect of selective photothermolysis which is that melanin in the hair absorbs the laser energy, converts it into heat and transfers it to the structures of hair thus causing coagulation. However, this method of hair removal encounters a few problems.

The main problem is the level of patient skin pigmentation as melanin, the main chromophore by means of which hair removal works is found not only in the hair but also in the skin. Thereby the probability of laser energy being absorbed by the melanin in the skin and the hair does not differ. Moreover, since the hair has a very small size compared to a laser spot on the skin, it becomes clear that the bulk of the laser energy will be absorbed not by the melanin in the hair but by the melanin in the skin. A consequence of this is that the skin heating up to coagulation.

The first lasers for hair removal were ruby lasers. The efficiency of ruby laser energy absorption (694 nm) is significantly higher than the efficiency of energy absorption of other lasers operating in the “transparent window” of the skin. However, gradually ruby lasers have been withdrawn because such efficient absorption by melanin has a downside. Melanin in the epidermis absorbs laser energy more efficiently thus overheating the epidermis and shielding hair from exposure.

Later for hair removal purposes neodymium, diode and alexandrite lasers were used. The efficiency of laser energy absorption of these lasers is lower than that of ruby, so in order to transfer to the hair the amount of energy sufficient for its coagulation it was necessary to significantly increase laser pulse energy. The result, as is clear from the above mentioned, is increased skin heating. Considering that with less effective absorption by melanin the depth of laser energy penetration into the skin increases, then, in this case, excessive heating of surrounding tissues is likely to lead to scarring.

Additional cooling devices used to improve treatment “tolerability” not only do not solve the problem but on the contrary, increase the risk of scarring as only the surface of the skin can be cooled but scarring occurs when overheating deep layers of the dermis.

In the development of a new method of laser hair removal, the main goal was to achieve high efficiency of hair removal while minimally damaging the surrounding tissues.

A special type of generation introduced in MULTILINE™ laser for hair removal is a train of nanosecond pulses with carefully selected parameters: total duration of a train, duration and energy value of every pulse and also an interval between the pulses. Parameters of the train are selected in such a way that during laser exposure the skin temperature varies around its normal value while the temperature of the hair gradually increases up to coagulation temperature. Also, absorption of nanosecond pulses by melanin-containing structures leads to the formation of acoustic waves which are powerful enough to destroy the hair but are not so to injure surrounding tissues. Therefore, the combination of thermal and physical impact on hair at relatively low density helps to achieve brilliant results of hair removal without the risk of damaging surrounding tissues.