1 Hair has 3 growth stages: Growth - 3-5 years; Resting 2-4 months as the hair root moves up to the scalp surface; and Shedding when the hair is shed from the scalp. Approximately 12% of hair is shedding at any time.
2 The hair follicle shape (round to oval) determines whether hair is straight, wavy or curly and its size determines hair thickness.
3 The outer layer of cuticles on each hair strand overlap each other like roof tiles and point downwards. When hair is wet the tiles raise up a little making them easy to damage. Cuticles damage with friction, dying and UVA and UVB light. Conditioners and oils coat the surface and seal damaged areas.
4 The shininess of hair is caused by the way light hits the cuticles. It is harder to make wavy and curly hair shiny due to this so shininess of hair is not always the best way to judge hair condition.
5 Tangled hair can be caused by sleeping or towel drying and is not necessarily a sign of bad condition. Squeeze water out of long hair or shake water out rather than towel drying.
6 Hard water can cause metallic ions build up on strands making hair feel rough. - Look for EDTA in shampoos which binds the metals and removes the build up if you are in a hard water area.. Frequent use of styling products and intense conditioners can also cause build up on hair but can be washed off with shampoos that don't contain silicones or conditioning agents.
Source - Swiftcraftymonkey blog by Cosmetic Chemist Susan Barclay Nichols