Laser Hair Growth Glossary: Every Term Explained

Anagen. The growth phase of a hair follicle, lasting two to six years. Laser therapy aims to keep follicles in anagen longer.

Androgenetic alopecia. Genetic pattern hair loss in men and women, driven by follicle sensitivity to DHT. The condition home laser devices are FDA-cleared to treat. See androgenetic alopecia explained.

ATP. Adenosine triphosphate, the energy currency of cells. Red light is thought to increase ATP production in follicle cells.

Catagen. The short transition phase between growth and rest.

Coherent light. Light whose waves are in step, as from a laser. LEDs produce incoherent light. See lasers vs LEDs.

Coverage. How much of the scalp a device treats in one session. Depends on light-source count and layout.

DHT (dihydrotestosterone). The hormone that miniaturises sensitive follicles in pattern hair loss.

Diode. A single laser or LED light source. Device "laser counts" are diode counts.

FDA-cleared. Permitted for sale via the 510(k) pathway as substantially equivalent to an existing device. Not the same as FDA-approved. See FDA-cleared vs FDA-approved.

Finasteride. An oral prescription drug for men that lowers DHT.

Hands-free. A device that treats without being held or moved — helmets and caps, but not combs or bands.

LED. Light-emitting diode; a wide-spread, incoherent light source.

LLLT. Low-level laser therapy. See what is LLLT.

Ludwig scale. The three-stage scale for female pattern hair loss. See Norwood and Ludwig scales.

Miniaturisation. The progressive shrinking of follicles so hairs grow finer and shorter.

Minoxidil. A topical medication for men and women that extends the growth phase. Often combined with laser therapy.

Norwood scale. The seven-stage scale for male pattern hair loss.

Photobiomodulation. The cellular response to light that underlies LLLT. See how laser hair therapy works.

Session. One treatment. Device schedules range from 90 seconds to 30 minutes, from twice a week to daily.

Sham device. An inactive look-alike used as the control in clinical trials.

Shedding (initial). A temporary increase in hair fall in the first weeks of treatment as follicles reset their cycle.

Telogen. The resting phase before a hair sheds.

Telogen effluvium. Diffuse shedding after stress, illness or childbirth; usually temporary, and not what laser devices treat.

Wavelength. The colour of the light in nanometres; home devices use about 630–680 nm. See wavelengths explained.