RESUMO
<p><b>OBJECTIVE</b>To investigate the changes of hair dermal papilla and its regulatory role in the growth cycle of the hair follicles.</p><p><b>METHODS</b>Single hair follicles were isolated from surgical specimens of human scalp and cultured in Williams E medium. The growth of the hair follicle was measured and the morphology and structure of the dermal papilla in the different growth cycles were observed continuously.</p><p><b>RESULTS</b>The hair follicle could grow in the medium for 12 days at the average growth rate of 0.2-0.3 mm/day. The flat and round dermal papilla lay at the bottom of the hair bulb in the telogen and anagen stages. In the hair follicle with accelerated growth, the dermal papilla became elongated, loosened, and closely adhered to the hair matrix. In the catagen stage the dermal papilla shrunk, and became separated from the hair matrix. A new hair bulb was regenerated when the hair follicle was transected at a low level. The hair follicle stopped growing after transection at a higher position.</p><p><b>CONCLUSION</b>The hair dermal papilla is the essential for hair follicle growth, and plays an important role in regulating the hair growth cycle.</p>
