There are two major types of hair: terminal hairs and vellus hairs.  Terminal hairs are thick, long, and usually pigmented with melanin.  These include the hair on the scalp, underarms, genitals, and eyebrows.  Hair from the chest, back, legs, and arms may also be terminal hairs.  Vellus hairs or “peach fuzz” are short and non-pigmented and can be found in most other areas of the body and face.  Lasers target terminal hairs with the pigment melanin.

Lasers target the melanin in the “bulge” and papilla region.  The bulge area of the hair follicle is important in the cycling and regeneration of hair.  The papilla is an extremely vascular region of the follicle and provides nutrients and oxygen to the other areas.  These regions need to be severely disabled for permanent destruction of the hair follicle to occur.

There are three phases of hair growth: anagen, catagen, and telogen.  Lasers can only target the anagen, or active, phase of the growth cycle.  Anywhere from 20 to 85% of hair is in the anagen phase at any given time.  This varies with different areas of the body.  Regression begins in the catagen cycle.  During the telogen stage, the follicle is “dormant” and prepares for the development of new hair.  Because the laser can only treat hairs in the anagen phase, several treatments will be necessary for the desired result. 

Lasers remove hair by the process of selective photothermolysis.  The light energy from the laser is transferred to thermal energy in the hair follicle.  The laser targets melanin, or the pigmented regions of the follicle.  When the thermal energy, or heat, is absorbed by the melanin in the cell structures (namely the bulge and papilla) they are destroyed.  All lasers also come with a cooling mechanism that prevents damage to the surrounding cells.

All lasers used in hair removal have the same basic mechanism of action.  There is not one laser, however, that is ideal for treating all patients; thus the need for multiple lasers and an experienced physician who can assess the best method of treatment.