Hair casts, also known as pseudonits, represent remnants of the inner root sheath, and often occur in great numbers and may mimic nits in the scalp.[1]: 764
Hair casts are distinct, solid, shining, white, freely mobile, tubular accretions that measure 2 to 7 mm in length and wrap the scalp's hair shafts.[2]
According to research using electron microscopy, the real peripillous hair casts are typically constituted of the exterior root sheath, with the internal root sheath occurring infrequently. Some are even composed of both the internal and external sheaths.[4]
Coaltar or keratolitic shampoo treatment is not effective. The best results are obtained when the cylinders are manually removed using a comb and a 0.025% retinoic acid solution.[3]
Scott, Michael J.; Roenigk, Henry H. (1983). "Hair casts: Classification, staining characteristics, and differential diagnosis". Journal of the American Academy of Dermatology. 8 (1). Elsevier BV: 27–32. doi:10.1016/s0190-9622(83)70003-4. ISSN0190-9622.
