Science of Laser Hair Removal

Some Key Terms

Anagen – the active phase of the hair growth cycle.  It is in this phase of growth that hair will respond to laser treatment.  Anywhere from 20% to 85% of hair can be in this phase at any given time.

Catagen- intermediate phase between going from the active growth phase to its regression into a dormant phase.

Telogen – the dormant phase of hair growth, in which the follicle prepares for the growth of new hair.

Chromophore – part of the follicle that absorbs light.  In hair removal lasers, the chromophore is melanin.

Electromagnetic Spectrum – the entire range of electromagnetic radiation, divided into 7 categories by wavelength.  Hair removal laser light is typically visible or infra-red.  The wavelength determines the type of hair and skin that may be treated.

Fluence - the amount of energy delivered to a given area.  Higher fluences may achieve greater results, but at the risk of greater thermal damage. 

Pulse duration - the length of time that energy from the laser is applied to the targeted tissue. 

Spot size – the area that a laser is capable of treating with each pulse.  At least 3-5 mm is required for effective hair removal. 

Terminal Hairs – thick, usually dark hairs on the body typically found on the scalp, pubic regions and eyebrows.

Vellus Hairs – thin, light-colored hair often referred to as peach fuzz.  This type of hair is largely untreatable by hair removal lasers.