Hair disorders associated with hair loss are discussed in Hair Loss and Its Causes. Hair shaft abnormalities can be attributed to both genetic are and physical or chemical damage to the hair.
All scalp hair undergoes some degree of physical and/or chemical damage in the 2 to 8 years of its growth. Physical and chemical stresses damage the cuticle (outer, protective layer) of the hair shaft (see Hair as a Biologic Fiber).
Physical damage typically is associated with stresses such as:
- long-term braiding or corn-rowing,
- hard brushing and combing,
- permanent waving, and
- excessive exposure to ultraviolet radiation in sunlight.
Chemical damage typically is associated with:
- use of chemical straighteners,
- curling and waving chemicals, and
- excessive exposure to salt water and ultraviolet radiation ("surfer's hair").
Hair Loss and Its Causes