Norwood scale

The Hamilton–Norwood scale (also known as the Norwood–Hamilton scale or simply the Norwood scale) is the most widely used classification system for male pattern baldness (androgenetic alopecia). The scale classifies the progression of hair loss into seven stages, numbered 1 through 7, with additional Type A variants describing cases where hair loss occurs primarily from front to back without distinct vertex involvement. The classification was first introduced by James B. Hamilton in 1951, who described the basic patterns and relationship between androgens and hair loss. In 1975, O'Tar Norwood revised and expanded the system, refining the stage definitions and adding the Type A variants to account for patterns that did not fit Hamilton's original scheme. The scale is regularly used by dermatologists and hair restoration surgeons to assess the severity of baldness, plan treatment, and track progression over time. However, its reliability has been questioned, as inter-examiner agreement can vary.