Q. How can lasers be used for so many different skin treatments?

A. Lasers have been touted for getting rid of a multitude of problems: excess hair, wrinkles, acne, skin discoloration, varicose veins, fungal infections, and regrettable tattoos. How can one technology have so many uses?

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“It seems like magic but it’s not,” says Deborah Scott, director of the Laser and Skin Health Center at Brigham and Women’s Hospital. It comes down to the physics of how lasers interact with skin and hair. A laser emits intense light at just one wavelength. Depending on the wavelength, the light is absorbed by specific molecules in skin or hair. The light is transformed to heat, which destroys structures containing a lot of the target molecules. “Lasers are very, very selective forms of destruction,” Scott says. “You pick a target and you only affect that target. So you don’t get a lot of scarring or collateral damage.”

Lasers for hair removal, for instance, target the pigment melanin in the hair shaft, which eliminates the hair and over time can destroy the follicle, resulting in permanent hair loss. Lasers for varicose veins target hemoglobin in the blood, and lasers for aging target water in skin cells, which Scott says can stimulate collagen production.

A knowledge of laser design and safety is important; for instance, a different setting may be required for a melanin-targeting laser in a person with dark skin. While lasers help many people, Scott says, “sometimes the results are not as dramatic as we hoped.”