Pseudopili annulati is a newly discovered anomaly of human hair which mimics clinical features of classical pili annulati but has an entirely different physical basis. Both are characterized by appearance of periodic bright bands along hair shafts viewed by reflected light. With pili annulati, banding is due to light scattered from abnormal, internal defects in hair shafts. With pseudopili annulati banding is found to be entirely a superficial effect. Fibers have elliptical cross-sections and are partially twisted with an oscillatory period along the fiber axis of 1 to 2 mm. Flattened external surfaces act as variably oriented mirrors to reflect light, and hair shafts themselves behave as cylindrical lenses which vary along the hair axis to periodically concentrate light for reflection from within the hair shaft. Pseudopili annulati probably is an unusual variant of normal hair.
Price VH, Thomas RS, Jones FT. Pseudopili AnnulatiAn Unusual Variant of Normal Hair. Arch Dermatol. 1970;102(4):354-358. doi:10.1001/archderm.1970.04000100002002