| BALDNESS | opINIoN americans
spend more than $35billion per year on a range of treatments for hair loss.
the hair fibre and the root sheaths. The pear‑shaped dermal papilla consists of a small group of fibroblast cells which are involved in regulating the production of the keratin hair fibre. The main function of the root sheaths is to protect the hair fibre as it develops. Two other structures associated with the hair follicle are the sebaceous gland, which produces a mixture of waxes and oils called sebum that acts to waterproof the hair, and the arrector pili muscle, which as its name suggests is responsible for piloerection, or erection of the hair. The hair shaft grows at a rate of
addition, a handful of other medicines are currently in development.
Hair and hair loss Before discussing the medicines used in the management of hair loss, it is helpful to take a brief look at the normal anatomy and physiology of hair. There are two distinct parts of any hair: the shaft, which is visible above the skin, and the follicle, which lies within the upper layers of the skin. The shaft is essentially composed of dead cells containing the structural protein keratin, plus a pigment known as
melanin. In addition, the shaft contains between 10% and 15% water, which helps maintain its appearance. In fact, three distinct regions of the
hair shaft can be discerned: the outer cuticle, which performs a mainly protective function; the cortex, the cells of which contain bundles of hair proteins as well as pigment granules and other structures; and the central medulla, which consists of large, loosely connected keratinised cells. The hair follicle can also be divided into three main parts, the dermal papilla,
approximately 1 cm per month, and each hair can last for up to 8 years. There are three phases of hair growth. The longest phase is called anagen, the duration of which determines the ultimate length of the hair. Epidermal cells surrounding the dermal papilla continually divide to produce new cells, with the older cells and the keratin they contain being pushed upwards to form the hair shaft. Eventually, the cells at the lower end
of the follicle begin to die, marking the onset of the next phase of hair growth, catagen. During this phase the dermal papilla shrinks and moves upwards through the skin, while at the same time the cells of the root sheaths stop dividing. Within a relatively short time the hair progresses to telogen, which is the resting phase of hair growth. During this phase the accumulation of cells around the hair fibre in the follicle leads to the formation of a ‘club hair’, which is easily detached from the scalp. Telogen
prime-journal.com | May 2011 ❚ 69
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