How Do Lasers Work on the Skin?

From movies like “Austin Powers” to “James Bond,” lasers have taken on a mystical lore for their powers. Dermatologists use them frequently on patients, and lasers have become one of the most popular devices used for skin care.^[1] They are versatile and the science about how they work is pretty fascinating. 

Lasers Selectively Target the Skin

There are different types of lasers based on the kind of light that they emit. The physics behind this is due to different naturally occurring crystals in nature. A crystal can be put into an activated state, and then release light as the crystal relaxes from the activated state. What this means is that lasers can release a very narrow band of light that is specific to the crystal used in the laser, and this light can selectively target different parts of the skin. Some of the targets include:

1) Blood vessels

Examples: Pulse-Dye laser, Nd:YAG laser

Lasers target the hemoglobin in the blood. By targeting hemoglobin, lasers can destroy blood vessels effectively. Cosmetically, these lasers can reduce the appearance of blood vessels that show up on the face due to chronic sun damage or rosacea. On the legs, these lasers can be used to treat unsightly spider veins. Medically, these lasers can be used to target lesions like warts (the laser targets the blood vessels in the wart) and hemangiomas (abnormal non-cancerous growth of blood vessels). 

2) Hair

Examples: Alexandrite laser, Nd:YAG laser, Diode laser

Lasers target skin pigment, known as melanin. Therefore, darker hair with more pigment absorbs the laser energy better and is destroyed more easily. In fact, white hairs are not targeted well by lasers. Apart from our hairs, our skin has pigment as well, and lasers are carefully selected and used so that the hairs are targeted but damage to the skin is minimized. Lasers may not permanently remove hairs but they can reduce their size so that they grow much slower and are less visible. 

3) Skin pigment

Example: Nd:YAG laser

Similar to hair reduction, lasers target the melanin pigment in the skin to destroy dark lesions in the skin. However, it’s not entirely that simple. Lasers should not be used to target a skin cancer like melanoma or a lesion that is more than just a change in pigment. That is why it is important to have a dermatologist look at the lesions first to confirm the diagnosis if cancer is a potential concern. A few examples of skin lesions that may look like just a little skin pigment, but are actually more, include a melanoma (which is a deadly skin cancer) or a seborrheic keratosis (a benign non-cancerous growth that is more than just pigment change). Lasers may be effective in treating non-cancerous, unwanted pigmented lesions like lentigines (known as sunspots) and melasma.^[2,3] 

4) Water

Example: Carbon dioxide laser, Er:YAG laser

The skin is mostly made up of water. Lasers that target water can be used to resurface and rejuvenate collagen production in the skin. By targeting water, these lasers create zones of microinjury that stimulate the production of collagen. This production of collagen can replenish lost collagen, and lead to an improvement in the appearance of wrinkles.^[4,5]

Lighter vs Darker Skin

It is very important to take skin pigment level into account when designing the right laser treatment. Darker skin will absorb pigment differently and have a greater risk for skin darkening (known as hyperpigmentation), skin lightening (known as hypopigmentation), blistering, and scarring. Certain lasers will not be good choices for darker skin and the setting needs to be chosen carefully.

Are Lasers the Same as Intense Pulsed Light?

No. They are not the same thing. Intense pulsed light sends a broad pulse of light that is filtered before it is delivered to the skin. Lasers are different in that a crystal is activated to deliver a very narrow band of light energy to the skin. The reason that this matters is that intense pulse light is like a jack-of-all-trades, and it can be used for many different treatments and skin targets. Intense pulsed light is not as efficient or effective towards a single target as a laser can be.