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This is an extremely abbreviated description of the terms and scientific concepts needed for consumers to understand how laser hair removal works. The endnotes contain an overview of the basic mechanics behind lasers. [1] For a detailed technical discussion of terms and concepts in laser hair removal, please read the excellent article by Dr. E. Victor Ross and colleagues. [2]
Light is absorbed by dark objects. If there’s enough light, something dark can get pretty hot (like the hood of a black car in the summer sun). In a similar way, 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.
The primary principle behind laser hair removal is selective photothermolysis. [3] 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. Laser and light-based methods are sometimes called phototricholysis or photoepilation.
Melanin is considered the primary chromophore for most lasers currently on the U.S. market. Hair removal lasers selectively target one of three chromophores:
Carbon, which is introduced into the follicle by rubbing a carbon-based lotion into the skin following waxing (this lotion is an exogenous chromophore). When irradiated by an Nd:YAG laser, the carbon causes a shock wave capable of mechanically damaging nearby cells. [4] 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. [5] Melanin, which 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).
Laser parameters that affect results
Several wavelengths of laser energy have been used for hair removal, from visible light to near-infrared radiation. These lasers are usually defined by the lasing medium used to create the wavelength (measured in nanometers (nm)):
Argon: 488 or 514.5 nm Ruby: 694 nm Alexandrite: 755 nm Pulsed diode array: 810 nm Nd:YAG: 1064 nm
Pulsewidth is an important consideration. It has been observed in some published studies that longer pulsewidths may be more effective with less side effects. Recently, very long pulse or super long pulse lasers have been theorized to be safer for darker skin, but this has yet to be demonstrated in published data.
Spot size, or the width of the laser beam, affects treatment. Theoretically, the width of the ideal beam is about four times the as wide as the target is deep. Most lasers have a round spot about the size of your little finger (8-10 mm).
Fluence or energy level is another important consideration. Fluence is measured in Joules per square centimeter, (J/cm2)
Repetition rate is believed to have a cumulative effect, based on the concept of thermal relaxation time. [6, 7] Shooting two or three pulses at the same target with a specific delay between pulses can cause a slight improvement in the heating of an area.
Epidermal cooling has been determined to allow higher fluences and reduce pain and side effects. Four types of cooling have been developed:
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