- Tiny indentations in the skin
- Comprised of living cells where the hair grows. The root sheath protrudes through the top layer of skin and is the point of exit for the hair shaft through the skin.
- Located next to the hair follicle within the dermis. Sebaceous glands secrete sebum, oils that lubricate the hair strand.
Hair has three regions:
- Root: Grows in the hair follicle. It is the widest part of the hair
- Shaft: The middle of the hair (from the root to the tip), where the hair tapers
- Tip: The end of the hair. The hair is narrowest at the tip
3 Layers of the shaft
- The outermost layer of hair. It looks like a series of overlapping scales. The layer is composed of a protein called keratin.
- The innermost layer. It is made up of cells that form a shaft in the middle. Different amounts of medulla may be present in the hair.
- Located between cuticle and medulla (Surrounds the medulla). Made of spindle-shaped cells and pigment granules (these give color to the hair). Contains ovoid bodies (look like large pigment granules) and cortical fusi (small bubble-like structures) in the cortex.
Growth Stages of the Hair
- Hair grows in a cyclic pattern that includes three stages (anagen, catagen, and telogen). The duration of each phase varies from strand to strand. New hair is always growing and may even grow in the same follicle as visible hair prior to shedding.
- The active growth phase of hair. Stage last three to five years (90% of the cycle).
- It is the second stage in hair growth, considered transition stage. Hair grows at this stage at a lower speed compared to anagen. The root bulb looks elongated due to being pushed out of the follicle.
- The last stage of hair growth cycle. In this phase, the hair follicle is resting (hair follicle is in stasis). In this stage, there is no new growth and the current strand sheds after one hundred days.