Page 4 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Terms used when discussing hair
Hair
Most people think of a hair as the hair shaft which sticks out of the
skin surface. However, this is only the visible part of the structure.
Follicle
A hair follicle is the structure which contains all constituents of the hair – it is an ‘indentation’ into the epidermis/dermis and is usually connected to a sebaceous gland and an arrector pili muscle. The follicle consists of the infundibulum, the isthmus and the bulb.
Growth
Follicles go through a number of growth phases:
Anagen
The anagen phase is known as the proliferation phase when a new
hair shaft is generated. This phase can last from a few weeks to years, on the scalp. Recent clinical research indicates that the anagen phase may consist of six distinct parts, A1 to A6.
Catagen
The catagen phase is the ‘transition’ phase when the hair stops actively growing. The follicle effectively shrinks in size as it regresses towards the surface. It usually lasts around two to three weeks, for all follicles.
Telogen
The telogen phase is known as the resting phase. During this time the follicle is relatively inactive and the hair is effectively dead. This phase can last between a few weeks and a few months, depending on the body area.
Exogen
The exogen phase is when the hair finally sheds – it falls out of the follicle under its own volition.
Kenogen
The kenogen phase is the time between the end of the exogen phase
and the start of the next anagen phase. The follicle is essentially empty of hair during this time. Androgenetic alopecia occurs when this phase is extended.
Hair shaft
The hair shaft consists of the inner core which is known as the medulla. This is surrounded by the cortex, which makes up most of the shaft.
Bulge
The bulge is the part of the follicle where the stem cells reside when
inactive. It exists between about one third to one half of the way down the follicle, usually located at the insertion point of the arrector pili muscle. In many follicles, this is around 1.0 to 1.5 mm from the skin surface.
________________________________________________________________________ 4 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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