The Cohen Hair Loss Classification System

In 2009, Dr. Bernard Cohen proposed a revised system for classifying stages of androgenetic alopecia, aiming to address the limitations of the 50-year-old Hamilton and Norwood (H-N) system. The Cohen system uses numbers instead of words to identify scalp topography and scores hair loss on a scale from 1 to 100. It includes a topographic map defining distinct areas of the scalp affected by androgenetic alopecia and a display chart with 100 blank cells divided into 3 general regions and 8 numbered zones. The severity of hair loss is assessed by comparing visible hair to visible skin, with the ratio placed into one of six categories. The system is adaptable to an infinite number of density and distribution patterns, both male and female. It should be noted that the system quantifies visible hair loss, not actual hair loss, as a zone with "minimal" loss has already lost 50% of its hair before the loss is visible to the naked eye.