الفهرس 
cover EnglishOnly 14 pages are availabe for public view
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Abstract
Hair is a dermal appendage found almost everywhere on the human body except the palms, soles and lips. Vellus hair are fine colorless hair covering most of the body except those areas covered with terminal hair, which are coarse pigmented hair found on the scalp and eyebrows. Vellus hair can transform into terminal hair when stimulated by androgens (male sex hormones), especially those on the face, back, chest, abdomen, axillae and genitalia at puberty. (Schlake, 2007)The hair shaft is composed of the protein keratin and is produced in the lower part of the follicle or bulb. The middle of the follicle contains the opening for sebaceous gland, the attachment of the erector pili muscle, and thickened area in the root sheath called the ”bulge” which is believed to contain stem cells important for regeneration of the hair follicle. (Bernard, 2005)Melanin is the pigment which gives both hair and skins its color. Much more melanin is present in hair than in skin, and this property allows relatively more absorption of laser light energy in hair than in skin. Hair color is determined not only by the absolute amount of melanin, but by the relative amounts of black-brown (eumelanin) and reddish brown (pheomelanin), and refraction of light within the layers of the hair shaft itself. (Gault et al, 1999)Hair growth occurs in cycles throughout an individual’s lifetime. Active hair growth is called anagen, and the length of the anagen phase determines the length of the hair. Scalp hair may remain in the anagen for up to 3 years, hair follicles then enter catagen, a phase of regression which lasts of a few weeks. The telogen, or resting phase, can last for months, depending inversely on the number of actively growing hair in the area.