6.5.4.1 Dermal Safety
Based on the hair removal mechanism of various lasers, the severity and frequency of dermal side effects are directly related to the fluence dose of the laser energy and the skin pigmentation levels. For safe and effective hair removal treatment, the treating clinician generally adjusts the laser parameters for each subject based on the hair and skin color. In addition, the contact surface material (typically sapphire) of the hand piece, skin cooling, and the clinician experience all play a part in providing a safe and effective treatment. Generally, the amount of laser energy (fluence) delivered is selected based on the patient’s Fitzpatrick skin type, or the skin pigmentation level. Care is taken to avoid excessive heating of the epidermal surface. An actively cooled sapphire tip may be used to provide heat conduction from epidermis before, during, and after each laser pulse. For treatment, the hand piece is firmly placed on the skin for about 0.5 s to cool the surface (epidermis can be cooled in 0.2 s). By effectively protecting the epidermis, cooling allows higher laser energy to be delivered to the deeper follicle target. Gentle compression of the hand piece further brings the target follicle closer to the skin surface and is thought to result in a greater efficacy of the treatment. Compression can also blanch the underlying blood vessels, thus minimizing laser absorption by the competing chromophore oxyhemoglobin providing greater epidermal safety. The ruby, alexandrite, and diode laser systems are roughly equivalent in their efficacy and dermal safety profile, with a slight preference for ruby when treating lighter skin and darker hair, and for Nd:YAG when treating darker skin. Nd:YAG is slightly less efficient because of its lower melanin absorption index but is much safer on the darker skin types V and VI.