National report - For many hair removal indications, existing lasers perform well, an expert says.
The trick is matching technology to patients' needs and one's level of expertise, she tells Dermatology Times.
"We have the right lasers for treating dark-haired, light-skinned patients. But we still don't have the answer for white hair, or very thin, light brown hair in dark-skinned individuals," says Melanie C. Grossman, M.D., a New York-based dermatologist in private practice.
Most laser treatments for hair removal rest upon the theory of selective photothermolysis (Science. 1983 Apr 29;220(4596):524-527), Dr. Grossman says.
"If one chooses a wavelength of light which is selectively absorbed by the target within tissue, and exposes that target to light at the chosen wavelength for a time which is directly related to the size of the tissue (less than or equal to the thermal relaxation time of the target), provided one uses enough energy, one can irreversibly damage a target while sparing surrounding tissue," she explains.
In the case of hair follicles, Dr. Grossman says, "Melanin is the target."
It absorbs light throughout the visible and near-infrared spectrums, she adds. Types of lasers which target melanin include the long-pulsed ruby (694 nm, although none of these lasers are being sold in the United States), long-pulsed alexandrite (755 nm), long-pulsed diode (800 nm) and long-pulsed Nd:YAG lasers (1,064 nm), as well as flash lamp devices, Dr. Grossman says.
More recently, she says manufacturers also have introduced lasers that combine light sources with radiofrequency energy or suction, as well as tunable devices that allow one to select different wavelengths for treating dark- and light-skinned patients.
Other means of removing hair could involve introducing exogenous targets that enhance destruction of the follicle, Dr. Grossman says.
"Photodynamic therapy (PDT) might allow us to do that," she says.
More specifically, Dr. Grossman notes that in a study she conducted, PDT with aminolevulinic acid (ALA) removed hair effectively, but it also tended to create hyperpigmentation.
"So far," she says, "nobody has been able to make that combination work effectively without side effects."
Similarly, she says the pigment enhancer Meladine (Creative Technologies) has not shown long-term effectiveness in laser hair reduction.
Select device according to need, skill
Choosing which laser best suits a particular indication requires one to consider parameters including spot size, wavelength, pulse duration, fluence and cooling, she says.
"It's not a question of which product is better. At this point, there are so many well-designed technologies that it depends largely on the person using the machine, and on the patient and area being treated. In the right hands, many different machines are effective," Dr. Grossman says.
Longer wavelengths are safer in dark skin because they offer less melanin absorption, she continues. "Short wavelengths have greater melanin absorption," Dr. Grossman says.
"Melanin absorption is critical to whether or not a laser will work. So if one wants to treat light hair, one wants to choose a wavelength that is very absorbent," Dr. Grossman explains.
Because light-haired patients usually have light skin, shorter wavelengths are generally safe and effective, she adds.
"However," she notes, "treating dark-skinned patients requires caution. The long-pulsed Nd:YAG lasers combined with cooling devices are safest for these patients."