This is the most common cause of hair loss. The development of genetic hair loss is associated with the shortening of the anagen (growing) phase of the hair cycle and consequently with an increase in the proportion of telogen (resting) hairs. There is a reduction in the size of the affected follicles, which results in a reduction in the diameter of the hairs that they produce. This is an essential feature of this type of hair loss, which accounts for the thinning of the hair and the widening of the partings.
Female genetic hair loss affects over 30% of women. The hair loss is typically diffuse (evenly spread over the scalp) and affects the frontal and vertex (crown) areas with similar severity. Often a band of slightly denser hair is retained along the frontal hairline. Also, women can exhibit a normal amount of hair in the front area of their scalp, which gradually thins out as you look farther back near their crown. Called a “Christmas-tree” look, this is also indicative of a genetic condition.
E. Ludwig categorized female genetic hair loss into three grades. Although other classifications have been developed, as with the Hamilton-Norwood scale for men, dermatologists, trichologists, and researchers most often use the Ludwig scale to categorize the type and extent of hair loss in women, devise an appropriate treatment and evaluate whether the condition is improving or worsening.
Source: Ludwig E. Classification of the types of androgenetic alopecia (common baldness) occurring in the female sex. British Journal of Dermatology, 1977; 97: 247-254.