What Happens to the Hair at the Microstructural Level During Laser Heating in Hair Removal. Hair is a complex keratin-based structure made up of several layers. In laser hair removal (808 nm diode laser), the energy is absorbed by melanin (the pigment) in the hair shaft and follicle, converted into heat, and causes thermal damage.
Let’s break it down step by step at the microstructural level.Brief Structure of the Hair
Hairs in catagen (transition) or telogen (resting) phases have much less melanin → weak or no effect.Visual Changes Under a Microscope
The laser does not simply “burn out” the hair.
It causes thermal denaturation of proteins and coagulation of melanin → the follicle is irreversibly damaged, and the hair stops growing permanently.
- Cuticle — the outermost layer, made of overlapping keratin scales (like roof tiles).
- Cortex — the main layer (80–90% of the hair), consists of α-keratin fibrils embedded in a matrix; this is where most of the melanin is located.
- Medulla — the central hollow core (present only in some thicker hairs).
- 50–60 °C (mild heating)
- Denaturation of proteins begins (α-keratin starts transforming into β-keratin).
- The cuticle slightly lifts, making the hair more brittle.
- Melanin heats up, but the follicle is not yet significantly damaged → temporary weakening of growth.
- 65–70 °C (the critical zone for effective hair removal)
- Complete denaturation of keratin in the cortex: the helical structure of the fibrils is destroyed, molecular bonds break apart.
- Melanin granules inside the cortex coagulate and break down.
- Stem cells in the bulge and matrix cells in the bulb of the follicle die from thermal shock → if the hair was in the anagen (growth) phase, it stops regrowing permanently.
- The cuticle is damaged → hair becomes dull and fragile.
- 80–100 °C and above
- Carbonization of melanin and keratin: proteins char, forming carbon residues.
- Vacuolization — steam bubbles form inside the cortex as water in the hair rapidly vaporizes.
- Total structural destruction: the hair essentially “explodes” from the inside, and the follicle undergoes necrosis.
- The characteristic smell of “burnt hair” comes from denatured keratin.
- Bulge — contains stem cells: at 70+ °C they are killed → no regeneration of new hair.
- Bulb — matrix cells (responsible for hair production): thermal coagulation stops cell division.
- Dermal papilla (vascular base): coagulation of tiny capillaries → the follicle is starved of nutrients.
Hairs in catagen (transition) or telogen (resting) phases have much less melanin → weak or no effect.Visual Changes Under a Microscope
- Before: smooth cuticle, dense and uniform cortex.
- After effective heating: cuticle lifts and peels off, cortex shows vacuoles (bubbles), melanin granules coagulate into dark clumps.
The laser does not simply “burn out” the hair.
It causes thermal denaturation of proteins and coagulation of melanin → the follicle is irreversibly damaged, and the hair stops growing permanently.
