Lichen planus hair loss, or lichen planopilaris, is a progressive inflammatory condition that causes permanent patchy hair loss, according to DermNet. The most common type is known as follicular lichen planus, and it generally develops along with lichen planus inflammation on the skin, mucosa and nails.
Lichen planus is characterized on the skin by purplish, flat-topped itchy bumps, and on mucous membranes as lacy white patches with occasional painful sores, according to the Mayo Clinic. The bumps are often polygonal, occurring most often at the ankles and wrists. Upon close inspection, these bumps may contain thin white lines known as Wickham's striae, which are what give the affected mucous membranes the characteristic lacy appearance, according to MedicineNet. It is an inflammatory condition caused by an abnormal immune response in which the immune system attacks the cells of the skin and mucous membranes; in the case of follicular lichen planus, the balding patches are marked by an absence of follicles, explains DermNet.
The cause of the abnormal immune response leading to lichen planus is yet unknown. While a correlation between lichen planus and hepatitis C infection of the liver has been noted, no causation has yet been proven, according to MedicineNet. Lichen planopilaris is most common among young adult women, though it can occur across a broad age range and is also found in men, according to DermNet.