Laser Hair Removal

Laser Hair Removal


How laser hair removal works


Frequently asked questions


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Laser Hair Removal

How laser hair removal works

The Chromophore

Laser removal of unwanted hair is carried out by transfer of laser energy to the hair follicle. This occurs by selective absorption of laser energy by the laser target, or chromophore, which absorbs the laser energy. This target is melanin, the pigment which is responsible for hair color. Melanin absorbs laser energy to a much greater extent than other skin structures. When laser energy is absorbed by melanin it is converted into heat.

The hair germinative apparatus

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Within the hair follicle lies the hair germinative apparatus, the structure responsible for producing hair growth. This hair germinative apparatus is surrounded by melanin, contained in the hair follicle. When laser energy is absorbed this causes a rapid rise in temperature. If enough laser energy is absorbed the temperature rise can cause irreversible destruction to the hair germinative apparatus, resulting in cessation of hair growth

Obstacles to overcome - Epidermal melanin

Melanin exists not only in the hair follicle (causing hair to have color), but also in the skin, resulting in skin color. Tanning is a result of extra melanin production by specialized cells, melanocytes, which produce melanin in response to sun exposure. The laser energy produced by the hair removal laser (usually a 755 nm. alexandrite laser) needs to pass through the epidermis to reach the hair follicle, which resides deeper within the skin. Therefore the laser energy will be partially absorbed by epidermal melanin before it reaches the hair follicle. So how is it possible for the laser to work? One must exploit the differential absorption characteristics of melanin in the hair follicle vs. epidermal melanin, and also exploit the differential cooling characteristics of these two structures.

Differential Absorption of Laser Energy based on melanin concentration

Melanin concentration in the hair follicle is much greater than in the epidermis. This is the reason that the hair is darker than the skin (for people with dark hair and light skin, or very black hair and brown skin). The higher melanin concentration in the hair follicle means that when exposed to laser energy the hair follicle will heat faster than the epidermis.

Differential Cooling - Hair follicle vs. epidermis

The hair removal lasers exploit another critical difference between the epidermis and the hair follicle beneath the skin surface - rates of cooling. The skin has a greater surface area compared to the cylindrical hair follicle, and will therefore cool faster. So not only does the hair follicle heat faster in response to laser energy, it will also cool slower. To further exploit this difference the skin surface can be cooled before, during, or after the laser pulse by applying either a cooling liquid (cryogen), cool air, or a cooled crystal. This will further reduce the temperature of the skin surface, allowing more energy to be delivered to the hair follicle without producing damage to the overlying skin.

Multipulsed lasers take advantage of the faster heating and slower cooling of the hair follicle vs. the epidermis

A further important refinement to many of the latest generation of hair removal lasers is the addition of multi-pulsing. These lasers take and divide the laser energy into a series of pulses, separated by milliseconds. Interruption of the laser pulse for these short intervals allows the epidermis to cool down while the hair follicle, which cools more slowly, remains hot. This allows the laser energy to be more effectively delivered to the hair follicle, while providing the skin with further protection. Not all lasers are multi-pulsed. Those that are not usually must use another method, such as a cryogen spray, to protect the skin.