In MPB, follicles slowly become miniaturized and the anagen (growth) phase of the hairs is reduced. Due to the shortened growing phase, the hair’s maximum length is reduced. At the same time, the telogen (resting) phase lengthens. This cycle slowly becomes more and more weighted toward the telogen phase
Over time, the anagen phase becomes so short that the new hairs do not even peek through the surface of the skin. Added to this, telogen hair growth is less well anchored to the scalp, explaining why there is often hair loss noted during showering
Miniaturization of the follicles causes the shaft of the hair to become thinner and thinner with each cycle of growth. Eventually, normal (terminal) hairs are reduced to villus hairs. Villus hairs are the soft, light hairs that typically cover a baby’s head.