Laser hair removal mechanism explained
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The laser hair removal mechanism is simple to comprehend. Understanding the laser hair removal mechanism is the first step in understanding how laser hair removal works. Laser hair removal mechanism is based on the type and way the laser is used. Laser hair removal mechanisms are discussed in detail in this article.
The monochromacity is one of the basic properties of laser which is essential for selective targeting of structures in the skin (chromophore), which preferentially absorb light of that wavelength and are destroyed by the following ways.
- Photo thermal destruction
- Photomechanical destruction
- Photochemical destruction
Photo thermal destruction
Selective thermal damage of a pigmented target structure results when sufficient
fluence at a specific wavelength is preferentially absorbed by the target, when
delivered during a time equal to or less than the thermal relaxation time of
the target.
The natural chromophore is the light absorbing pigment in the hair called melanin.
The melanin can absorb light in the visible-infrared region to target hair follicle.
Therefore, with the help of lasers hair shaft, hair follicle
and the heavily pigmented matrix can be effectively targeted by using lasers
having wavelengths in the 600- to 1100-nm region.
The two basic factors responsible of hair follicle destruction are;
- Selective absorption by melanin
- Deep penetration into the skin with hair follicle
The light energy of laser light is converted into the heat energy which is disrupting force for hair follicle. The different lasers with their respective wavelengths are
Selective photothermolysis
The term "selective photothermolysis" is frequently used to explain the effectiveness of photo thermal destruction of hair structures of the skin by lasers. By selective photothermolysis it is meant that the lasers selectively heat the targeted hair structures like hair shaft and hair follicle matrix. The adjoining skin is spared as it is theoretically invisible to laser and very little absorption of the laser energy in the adjoining skin takes place. The energy adsorbed by the hair follicles is high enough to disrupt it. In other words it is "thermolysed" by the laser light. Another important aspect is that the pulse duration of laser energy used should be shorter than the thermal relaxation of the target. It is the time taken by the target to cool by 50% of its peak temperature after it has been lasered.
Photomechanical destruction
Very short nanosecond pulses have been employed to target target hair follicles, as a result melanin in the hair shaft and hair follicles is selectively heated to very high temperatures. This generates photo-acoustic shock waves which are capable of causing focal photomechanical disruption of the melanocytes present in the hair follicle but as these are very low intensity they fail to cause complete follicular disruption. Q-switched 1064-nm Nd:YAG lasers are capable of acting through this type of mechanism.
Photochemical destruction
The third mechanism is photochemical destruction by use of laser light. The laser light energy causes a chemical reaction in the light sensitive material which gives chemicals which react with hair follicles and causes chemical damage to the hair shaft and hair follicle structures. Aminolevulinic acid is a chemical being used as photo sensitizer (increases light sensitivity) which upon absorbing a photon of laser light in 630nm range can cause up to 40% damage to hair. Other photodynamic agents are porphyrins, chlorins, phthalocyanines and phenothiazine.
