for Improving Appearance John E. Oblong and Cheri Millikin The Procter and Gamble Company, Cincinnati, OH, USA 2.1 Introduction 37 2.2 Basics of Skin Physiology 38 2.3 Changes in Skin Structure and Integrity as a Function of Environment and Aging 41 2.4 Photodamage to Skin 43 2.5 Intrinsic Aging of Skin 45 2.6 Treatment Effects […]

Because human hair plays important roles in social and sexual communication (discussed in Section 1.2), hair where it is unwanted or hair loss is a source of embarrassment and psy­chological distress. A variety of methods are available to help control both excess hair growth and hair loss. The earliest methods used to remove hair were […]

Specific effects of androgens on hair follicle cells. Androgens must alter many aspects of follicular cell activity to cause these changes in follicle and hair type. They must alter the ability of epithelial matrix cells to divide, determine whether they should differentiate into medulla (found in some large hairs), and regulate the pigment produced and/or […]

1.7.2.1 Human Hair Follicles Show Paradoxically Different Intrinsic Responses to Androgens Androgens’ dramatic stimulation of hair growth is seen first in puberty with pubic and axillary hair development in both sexes [16-18]. These changes parallel the rise in plasma androgens, occurring later in boys than girls [146, 147]. Testosterone stimulates beard growth in eunuchs and […]

Lynfield [143] found more scalp follicles were in anagen during the second and third trimesters (95%) and for about a week after birth; by six weeks this fell to about 76%, remaining low for 3 months. Pregnancy hormones maintain follicles in anagen, but after birth many enter catagen and telogen, causing a synchronised partial shedding […]

Apart from seasonal changes (Section 1.6), the most obvious regulators of human hair growth are androgens, as long as individuals have good nutrition [15,141] and normal thy­roid function [137,142]. Pregnancy hormones also effect hair growth causing diffuse hair loss post-partum.

Seasonal changes are much less obvious in human beings, where follicle cycles are gen­erally unsynchronised after age one, except in groups of three follicles called Demeijere trios [26]. Regular annual cycles in human scalp [11-13], beard, and other body hair [11] were only recognised relatively recently. Seasonal changes in hair growth were evident in 14 […]

Studies in many species, including sheep, hamsters, mink, and ground squirrels [105,106], show that long daylight hours initiate short periods of daily melatonin secretion by the pineal gland and summer coat development, while short (winter) day-length increases melatonin secretion and stimulates a longer, warmer pelage [7,103]. The pineal gland acts as a neuroendocrine transducer converting […]

Hair follicles are under hormonal regulation due to the importance of coordinating altera­tions in insulative and colour properties of a mammal’s coat to the environment or visibility to changes in sexual development. Seasonal changes usually occur twice a year in temperate regions with coordinated waves of growth and moulting to produce a thicker, warmer winter […]