1.1.1.1
Gurpreet S. Ahluwalia (ed.), Cosmetic Applications of Laser and Light-Based Systems, 3-35,
© 2009 William Andrew Inc.
1.2 Treatment of Hair Growth Disorders 25
References 26
The hair follicle is a highly dynamic organ found only in mammals. Although frequently overlooked, the follicle is fascinating from many viewpoints. For cell and developmental biologists it has an almost unique ability in mammals to regenerate itself, recapitulating many embryonic steps en route [1,2]. For zoologists, it is a mammalian characteristic, significant for their evolutionary success and crucial for the survival of many mammals-loss of fur or faulty colouration leads to death from cold or predation. Human follicles also pose a unique paradox for endocrinologists as the same hormones, androgens, cause stimulation of hair growth in many areas, while simultaneously inhibiting scalp follicles causing balding [3,4]. In contrast, hair is often seen as rather irrelevant medically, as human hair loss is not life threatening. Nevertheless, hair is very important for most people [5]. Many men spend significant time shaving daily and vast amounts are spent on hair products; a ‘bad hair day’ is a common expression for days when everything goes wrong! This reflects the important role hair plays in human communication in both social and sexual contexts and explains why hair disorders such as hirsutism (excessive hair growth) or alopecia (hair loss/ balding) cause serious psychological distress [6].
Hair growth is co-ordinated by hormones, usually in parallel to changes in the individual’s age and stage of development or environmental alterations like day-length [7]. Hormones instruct the follicle to undergo appropriate changes so that during the next hair cycle, the new hair produced differs in colour and/or size. This chapter will review the functions of hair, its structure and the processes occurring during the hair growth cycle, the changes which can occur with the seasons, and the importance of the main regulator of human hair growth, the androgens. Throughout the chapter, the main emphasis will be on human hair growth.