Page 4 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
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 germ 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.
Germ/Stem cells
All follicles have germ/stem cells which stimulate the anagen, growth phase of the follicle’s cycle. These are only active during the anagen phase and then remain quiescent inside the bulge for the rest of the growth cycle.
Hair matrix
Dermal papilla
Isthmus Infundibulum
Inner root sheath (IRS)
Outer root sheath (ORS)
This is the region where matrix keratinocytes grow the hair shaft. Melanocytes are located here which provide the hair with its colour.
The capillaries which feed the follicle with blood are located in the dermal papilla.
The isthmus is the portion between the sebaceous gland opening and the germ cell bulge.
The infundibulum is the upper portion of the follicle which extends from the surface down to the opening of the sebaceous gland. The IRS is formed of three layers of cells which shapes the hair shaft as it grows.
The ORS encases the hair shaft and IRS and extends from the bulb up to the epidermis.
Melanin
Melanin is the substance which is formed by the melanocytes and gives the hair (and skin) its colour. The melanin is mostly found inside the hair shaft and is the target chromophore for all photothermal treatments with lasers and IPLs.
Hair bulb
This is located at the inferior (lowest) part of the follicle. The bulb contains the follicular matrix surrounding the sides and top of the dermal papilla.
Table 1 – General terms and expressions used when discussing hair
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