Hair Casts

Example 2

Hair casts or 'pseudonits' are thin, elongated, cylindrical concretions that encircle the hair shaft. Hair casts range in size from 2-7 mm and can be easily dislodged. Hair casts can be easily differentiated from "knits" because they slide along hairs when grabbed with the fingers. They are usually asymptomatic and particularly common in young women. 
Casts have not been extensively studied, however, one study of over 3500 women showed that casts were seen in 60 % of women. Traction hairstyles, use of hair sprays and a variety of inflammation scalp conditions are associated with hair casts. They are not infectious or contagious.

Reference
Zhang W. Epidemiological and aetiological studies on hair casts. Clin Exp Dermatol. 1995;20:202-7.