Hair forms in a pouch like structure below the skin called a hair follicle. What we see as hair is actually the hair shaft, which is the keratinized, hardened tissue that grows from this follicle.

Humans have more hair follicles per square inch of skin than most higher primates, including chimpanzees and gorillas. Because most of this hair is fine and pale (called vellus hair), it usually is not visible to the naked eye. Consider this: the forehead has more hair follicles than any other part of the body. The thicker, fully pigmented hair most people consider “real hair” is called terminal hair. This hair is found on scalp, eyebrows, legs, backs and underarms.

Everyone’s hair grows differently, depending on age, weight, metabolism, hormones, ethnicity, medications and other factors. But all hair grows through three distinct growth phases:

1. Active growth phase (called the anagen phase), which lasts up to several years. At any given time, the majority (85%) of our body hair is in this phase. During anagen, the hair has an abundance of melanin.
2. Regressive phase (catagen phase), which lasts about two weeks, during which the hair stops growing but is not yet shed. About 3-4% of our body hair is in this phase at any given time.
3. Resting phase (telogen phase), which lasts 5-6 weeks, at the end of which the hair falls out and a new hair begins to form. Approximately 10-13% of our body hair is in this phase at any one time.

The laser most effectively disables hair that is in the active growth (anagen) phase.