To be defined as a laser, only one wavelength of light must be produced and when this light is absorbed by a specific target, the light turns into heat.

The heat then causes damage to the target. In the case of laser hair removal, many different types of laser are able to target hair and cause damage to the follicle, affecting its growth.

The main types of lasers in use today to remove hair are the ruby, alexandrite, diode and neodymium:YAG laser with multiple manufacturers of each.

The ruby, alexandrite and diode laser, despite having very different wavelengths of 694 nm, 755 nm and 800 nm respectively, all target the pigment in the hair (melanin). Because of this, these lasers do not treat white or gray hair since the pigment is reduced in these. These lasers also do not treat hair in dark skin without also removing the pigment in the skin--therefore, these lasers are not generally used in dark skinned individuals.

The neodymium:YAG laser has a much longer wavelength, 1064 nm, and does not target the melanin in the hair but appears to work through mechanical damage caused by the laser and thus can be used on multiple skin types and hair colors. However, this laser does not appear to have the same overall effectiveness in permanent hair reduction as the other lasers mentioned above.

One can also have a machine that generates multiple wavelengths of light function as a laser by the use of filters. This allows the machine to be used for multiple purposes, including hair removal, but these are not lasers in the truest sense of the definition.

Limitations

It is important to understand the limitations of laser hair removal. Hair has amazing regenerative properties -- just look at cancer survivors who lost their hair after multiple rounds of chemotherapy or radiation and had their hair grow back.

The ability of hair to regenerate has also been demonstrated . Hair has been able to regenerate over time in mouse experiments where various parts of the hair follicle are removed. In other experimentsjust a portion of the bottom of a mouse hair follicle, the dermal papilla, is placed in the pad ofthe mouse's foot where there is not normally any follicles and a new hair is generated.

It is extraordinarily difficult to permanently remove hair. It takes multiple treatments with any laser at relatively high fluence (power) to permanently inhibit hair growth. The hair must be actively growing to do the most damage and the laser power must be the highest possible without damaging the skin.

Therefore, the best subject with the greatest chance of a permanent decrease in hair is the person with light skin and dark hair so that the power used can be the maximum.

No laser promises permanent hair loss after even multiple treatments. The Food and Drug Administration (FDA) has allowed laser manufacturers to claim only the promise of permanent hair reduction, not permanent hair loss, with laser hair removal.

Permanent hair reduction is defined as hair growth that is retarded over the cycle of the hair growth in that area of the body. In general, it takes about a year for a hair follicle to completely cycle through its growth and rest phases so any assessment of how much hair removal has occurred must be assessed at the end of this time, ideally six months from the last treatment.

One of the things that happens frequently in laser hair removal is that the hair becomes finer but does not disappear completely. A realistic goal of laser hair removal is then, a long term reduction of the hair growth.

Alternatives

The alternatives to laser for hair removal are shaving, depilatories, waxing and electrolysis. Of these, electrolysis is the only one that offers the potential for permanent hair removal.

Like lasers, there are many different types of electrolysis and different capabilities and training of the individual electrologist.