mechanism of laser hair removal
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mechanism of laser hair removal
The primary principle behind laser hair removal is selective
photothermolysis. Lasers can cause localized damage by selectively heating dark
target matter in the area that causes hair growth while not heating the rest of
the skin. Light is absorbed by dark objects, so laser energy can be absorbed by
dark material in the skin (but with much more speed and intensity). This dark
target matter, or chromophore, can be naturally-occurring or artificially
introduced.
Hair removal lasers selectively target one of three chromophores:
Carbon, which is introduced into the hair follicle by rubbing a carbon-based
lotion into the skin following waxing (this lotion is an "exogenous
chromophore"). When irradiated by a Q-switched Nd:YAG laser, the carbon causes a
shock wave capable of mechanically damaging nearby cells. This method has been
abandoned since it does not cause permanent loss. (It has been replaced with the
long-pulsed Nd:YAG laser which targets endogenous melanin in the follicle.)
Hemoglobin, which occurs naturally in blood (it gives blood its red color).
It preferentially absorbs wavelengths from argons, and to a lesser extent from
rubies, alexandrites, and diodes. It minimally absorbs the Nd:YAG laser
wavelength. Hemoglobin is not a primary target for laser hair removal.
Melanin is considered the primary chromophore for all hair removal lasers
currently on the market. Melanin occurs naturally in the skin (it gives skin and
hair its color). There are two types of melanin in hair: eumelanin (which gives
hair brown or black color) and pheomelanin (which gives hair blonde or red
color). Because of the selective absorption of photons of laser light, only
black or brown hair can be removed.
Any laser light beam intended for
topical use can only penetrate skin tissue two millimeters deep. [citation
needed] As such, there has been great controversy surrounding the laser industry
claims to what most people think of when they hear the word "permanent".
The dermal papilla is the only appropriate target of destruction, as it is
the only substructure of the hair shaft which can reproduce a new root system,
and therefore a new hair shaft. [citation needed] The dermal papilla is located
at a depth of 7-8 millimeters for coarse hair, and so is beyond the reach of
laser.
For a short list of approved lasers, the Food and Drug Administration permits
the use of the phrase "permanent reduction." The use of the phrase "permanent
removal" is not permitted for any laser whatsoever. The intended meaning of
"permanent" may also be confusing to consumers. Most consumers understand
"permanent" to mean that the hair will stop growing forever. However the FDA
permits the use of "permanent" as long as the laser reduces some visibily
growing hairs for as short a time as one growth cycle (a matter of a few months
for most body parts). In fact, many clinical studies have shown the rate of hair
regrowth from laser epilation to be only slightly slower than from traditional
methods. No long term clinical studies (i.e., follow-up greater than 12 months)
have been done to test the true permanency of laser hair removal.
Clinics performing laser hair removal usually recommend at least six
treatments. For this reason treatments are often sold in packages.
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