The alexandrite laser wave length of 755 nm is absorbed about 20% less strongly by melanin compared with the ruby laser wavelength of 694 nm. Its absorption by the competing chromophore, oxyhemoglobin, is substantially increased as compared to the 694-nm wavelength. However, the longer wavelength of 755 nm penetrates more deeply into the dermis and is less absorbed by epidermal melanin. This theoretically decreases the risk of epidermal damage, especially in individuals with darker skin types.
Because dermal scattering decreases with increasingly longer wavelengths, 755-nm light penetrates deeper into tissue than does shorter wavelengths. In theory, the use of longer wavelengths should increase the ratio of energy deposited in the dermis relative to the epidermis. This would result in relatively increased bulb heating while at the same time promoting epidermal sparing (Ross et al. 1999).
The reported hair removal success rate using an alexandrite laser has ranged from 40 % to 80% at 6 months after several treatments (Gorgu et al. 2000) In a controlled randomized study using a single 20 J/cm², 5- to 20-ms alexandrite laser on various anatomic sites, investigators reported a 40% reduction in hair growth 6 months after treatment. This increased to >50% (on the upper lip) if a second treatment was performed after 8 weeks. In another study, one treatment with a variable pulsed alexandrite laser produced maximum hair growth reduction at 6 months of 40 %-56% for the lip, leg, and back. Finally, one study has noted a mean 74% bikini hair reduction 1 year after five alexandrite laser treatments.
David J. Goldberg