Male Pattern Baldness: The Norwood-Hamilton Scale
The most common form of baldness is a progressive hair thinning condition in males called Androgenic Alopecia or "Male Pattern Baldness".
The extent and pattern of male pattern baldness is often classified using a scale. Originally developed by Dr James Hamilton in the 1950s the pattern baldness classification system was modified to its current form by Dr O'Tar Norwood in the 1970s. Dr Norwood's basic scale of pattern baldness is illustrated and described as below.
Type I: The Type I pattern indicates minimal hair loss.
Type II: In Type II, there are usually limited areas of recession of the hair line at the temples.
Type III: Type III is primarily the first level on the scale that a dermatologist would regard as real pattern baldness and something that needs treatment. Most type three scalps have deeper symmetrical recession at the temples. The affected areas are bare or only sparsely covered by hair.
Type III [Vertex]: In this case, the hair loss happens from the vertex (the back of the head) and with only very limited hair line recession.
Type IV: With Type IV on the scale, the hair loss gets extensive. At this stage, there is sparse or no hair on the vertex. The hair line recession and the hair loss from the vertex are separated by a band of moderately dense hair that extends across the top. This band connects with the fully haired fringe on the sides of the scalp.
Type V: With development of Type V pattern hair loss, the vertex hair loss region is still separated from the fronto-temporal region but it is less distinct. Here, the band of surviving hair across the crown is narrower and sparser. The vertex and fronto-temporal regions of hair loss are bigger.
Type VI: In Type VI, the bridge of hair that crossed the crown is now gone with only some sparse hair remaining. The hair line recession and vertex hair loss areas now join together and the extent of hair loss is enormous.
Type VII: Type VII is the most severe form of hair loss. In people with this most extensive hair loss presentation, only a narrow band of hair in a horseshoe shape survives on the sides and back of the scalp. There is little or no hair on the top of the head and the frontal hair line no longer exists. Initial signs of balding are evident with an increased temporal recession accompanied by mid-frontal recession (Type II). Hair loss in a round area on the vertex follows, and the density of hair decreases, sometimes rapidly, over the top of the scalp (Types III-VII).