Hair color is genetically determined, and is a result of both the type and amount of melanin within the hair shaft. Melanin production occurs only during the anagen phase, by melanocytes in the bulb that transfer melanin granules to hair keratinocytes. Distinct types of melanosomes exist in hair of different colors. Dark hair contains large numbers of eumelanin granules, whereas light hair contains mostly pheomelanin. Red hair contains erythromelanin granules that are rich in pheomelanin. In gray hair, melano-cytes show degenerative changes such as vacuoles and poorly melanized melanosomes, whereas in white hair melanocytes are greatly reduced in number or are absent.
Most individuals demonstrate greater melanin density in their hair as compared to their skin epidermis such that the absorption coefficient of the hair shaft and bulb is roughly 2-6 times that of the epidermis. Thus, hair will generally absorb more of the melanin-absorbing wavelengths emitted from today's laser and light source hair removal systems.
Thus, color contrast between the epidermis and the hair shaft are paramount in determining the optimal wavelengths and pulse duration for successful treatment. For high contrast (dark hair and light skin) high fluences, shorter wavelengths, and relatively short pulse durations can be used without risking epidermal injury. Conversely, low contrast areas (dark hair and dark skin) require lower fluences, longer wavelengths, and longer pulse durations for safe treatment.
Was this article helpful?