The Biology of Hair Follicles

Hair has many useful biologic functions, including protection from the elements and dispersion of sweat-gland products (e.g., pheromones). It also has psychosocial importance in our society, and patients with hair loss (alopecia) (Table 1) or excessive hair growth often suffer tremendously. Not surprisingly, the demand for drugs that alter hair growth and appearance has led to a multibillion-dollar industry, yet few drugs that are effective for these purposes are available. However, recent progress in our understanding of the biology and pathology of hair follicles should lead to more effective therapies for disorders of hair growth. Structure and Function of Hair . . 

Lichen striatus: clinical and laboratory features of 115 children.

To analyze the clinical features, response to treatment, and follow-up of lichen striatus and any associated symptoms or disease, we designed a retrospective study involving 115 affected children at the Pediatric Dermatology Unit of the Department of Dermatology of the University of Bologna, Bologna, Italy. Between January 1989 and January 2000 we diagnosed lichen striatus in 37 boys and 78 girls (mean age 4 years 5 months). We studied their family history and the season of onset, morphology, distribution, extent, duration, histopathology, and treatment of their lichen striatus. We found that family history was negative in all our patients except for two pairs of siblings. The majority of children had the disease in the cold seasons; precipitating factors were found in only five cases. The most frequently involved sites were the limbs, with no substantial difference between upper and lower limb involvement. When lichen striatus was located on the trunk and face, it always followed Blaschko lines; in seven children the bands on the limbs appeared to be along the axial lines of Sherrington. In 70 cases, lichen striatus was associated with atopy. The mean duration of the disease was 6 months and relapses were observed in five children, and in one instance the disease had a prolonged course. Only a few case study series of lichen striatus in children have been reported and ours is the largest to date. The etiology of lichen striatus remains unknown in the majority of our patients. The confirmed association with atopy observed in our patients may be a predisposing factor. It has generally been accepted that lichen striatus follows the lines of Blaschko, and this distribution is a sign of both a topographic and a pathogenetic concept. In patients where lichen striatus is along axial lines, a locus minoris resistentiae, we suppose that this distribution may only be an illusory phenomenon in instances in which the trigger factor prefers this route, consisting of several successive Blaschko lines, but appearing as a single band