Physical principle – selective photothermolysis
The principle behind laser hair removal is based on what is known as selective photothermolysis. This involves using a laser to generate a highly concentrated beam of light at a specific wavelength. Each wavelength specifically targets a certain chromophore (absorbing substance) in the tissue. In hair removal, the relevant chromophore is melanin.
The emitted light penetrates through the top layer of skin into the depths of the hair follicle. There it encounters the melanin in the hair shaft and root, which has a particularly high absorption capacity. As a result, the melanin preferentially absorbs the energy of the light, while the surrounding tissue—e.g., blood vessels or water in the skin—is hardly affected, if at all.
The absorbed light energy is then converted into heat, creating temperatures of around 60–70 °C in the hair follicle. This temperature is sufficient to specifically damage the sensitive growth cells and structures in the hair root. The surrounding tissue is spared because it contains less or no melanin, and the heat is therefore selectively generated only in the pigmented structures. This targeted principle makes the method effective and relatively safe at the same time.
Target structure in the hair root
The key target structures in laser hair removal are the areas of the hair root that actively control hair growth. Melanin acts as a “light trap” here: it absorbs the laser energy and transfers the heat directly to the sensitive cell clusters.
Hair matrix: This is the zone directly above the dermal papilla, where highly active cells constantly divide to form new keratin for the hair shaft. If these matrix cells are destroyed, new hair can no longer be formed.
Dermal papilla: It contains blood vessels and nerves and is the control and supply center of the hair root. If it is damaged by heat, the supply to the matrix collapses, permanently stopping all hair production.
By targeting the melanin in the hair, laser light directs the necessary heat precisely to where the hair is formed and supplied. Permanent hair removal is only possible if both the hair matrix and the papilla are irreversibly destroyed.
