Lichen pilaris

Occasionally one sees, either alone or in conjunction with ordinary lichen, or other disease where the skin is hyperaemic, little elevations like papulae, which are, however, seated at the hair follicles; the hair in fact piercing the center of the papule. A distinct lump is felt by the finger. Hyperaemia of the follicular plexus is followed by fibrous deposit outside the follicile, forming a papule.

When this is accompanied by inflammatory deposit, then solid papules are formed at the hair follicles and constitute lichen pilaris.

Lichen pilaris is then "fibrous inflammation" seated at the upper part of the hair follicles, the effusion of plastic lymph taking place around the follicular walls, and producing, according to its degree, more or less well marked and distinct papulation, each elevation being perforated by a hair. It must not be confounded with pityriasis pilaris, which is merely a desquamation of cuticular cells into, and distending, the hair follicles, preventing the formation of the hair, and producing a blocking up of the follicles, the collected cells forming "a knot" in the upper part of each follicle, a state of things that may occur after pityriasis rubra, or as the result of an inactive state of skin, especially about the thighs, and which latter only needs the free use of soap and water for its removal.