Hair and Nails

About the Hair and Nails

Hair and nails are skin appendages made of keratin. Hair shafts grow from follicles in the dermis at approximately 1 cm per month on the scalp. The hair cycle has anagen growth 2 to 7 years on scalp, catagen regression 2 to 3 weeks, and telogen resting 3 months, with 50 to 100 hairs shed daily. Hair color comes from melanin: eumelanin brown black and pheomelanin red. Graying occurs when melanocytes die. Baldness androgenetic alopecia is hormone mediated, and drugs such as minoxidil and finasteride are used in its treatment. Nails grow at approximately 3 mm per month fingernails, 1 mm toenails, requiring 6 months for fingernail and 18 months for toenail replacement. The nail matrix produces the nail plate. The lunula is the visible white crescent at the nail base. Clubbing suggests chronic lung or heart disease. Spoon nails koilonychia suggest iron deficiency.