Summertime is nearly here and the lines are forming for last minute laser hair removal. Lasers are an effective way to permanently remove hair from underarms, legs, back, arms, chest, bikini area, and even faces. But how do they work?
Lasers take a substance such as argon gas, and pump energy into it, pushing the gas electrons up to higher energy levels. When the electrons fall back to their normal state, they release energy in the form of of light. When one photon of light hits another high-energy electron, it releases a second photon of light. Repeat this countless trillions of times in a closed, mirrored container and you have a tremendous amount of pent-up energy bouncing around.
You can imagine when you open the container, all this stored super-high energy light is released in one brilliant, powerful laser flash.
Lasers destroys things (such as hair, blood vessels, etc.) when their target absorbs the light and converts it to tremendous heat.
Brilliant work by Rox Anderson and Jon Parrish at Harvard helped us apply lasers to the skin. They figured out that different colors of light are absorbed selectively by different parts of the skin; they also discovered that changing the duration of the laser flash changed how it worked. So different colored lasers are used to target different areas (hair, blood vessels, etc.). To target tiny things like tattoo pigment, very short laser flashes are used; in contrast, longer, slower laser flashes are required to treat larger things, like blood vessels. For example, blood vessels are large and absorb green light; therefore, green, slow flashing lasers are often used to treat dilated blood vessels on the face.
The target for hair removal is not the hair itself but rather the brown pigment in it. Brown pigment absorbs red (and infrared light); therefore, lasers used to target hair are typically red. So how do you get a hair laser to hit the hair but not damage the same brown pigment in your skin? Easy. You protect the skin by super-cooling it first. The device fires a blast of cold air just before firing the laser. This super-cold air protects your skin from the laser, but the hair pigment deep in the skin is not protected and takes the full brunt of the laser.
The laser hits the hair pigment with a such an intense blast of energy that it explodes the hair follicle. This is why laser hair remove hurts a little — sort of like a rubber band being snapped against your skin.
It takes multiple treatments to remove the hair permanently because not all of the follicles are destroyed even after taking a hit from the laser. So if you want to get laser hair removal done, you should plan it months in advance. Tomorrow — Ten Things You Need to Know About Laser Hair Removal.
Photo credit: Steve Jurvetson