What is “paradoxical hypertrichosis” (increased hair growth) in laser hair removal, and in which areas is it most commonly seen?

Paradoxical hypertrichosis is a condition where, instead of reducing hair growth in an area treated with laser hair removal, fine vellus hairs are stimulated, thickening, darkening, and spreading. This side effect is commonly seen in areas with dense fine, weak hairs, such as the face, neck, shoulders, and upper arms. The primary cause is the application of an insufficient dose (low energy) of laser light to the fine hairs; the heat is insufficient to destroy the root, instead stimulating blood flow and stem cells, transforming the hair into a generic type. To avoid this risk, selecting the correct device and high wavelength is critical for areas like the face.