1.   A residue can build up on the hair shaft, leaving the hair limp and dull looking.

2.   Bathes the hair shafts.

3.   Chemical coloring involves the opening of the hair shaft to let in pigment.

4.   During the anagen phase, the follicles are adding keratin, a protein, to the base of the hair shaft so that it gets longer and longer.

5.   During electrolysis, sterilized needles are passed down the hair shaft to the follicle.

6.   Nits are tiny, rice-shaped, whitish pods that the mother louse cements with a special mucus to a hair shaft near the scalp.

7.   The eggs are coated with a gluelike substance that adheres them to the hair shaft.

8.   These packets are produced by cells called melanocytes in the hair bulb, where the hair shaft originates.

9.   These days, most conditioning products are formulated to seep into the hair shaft without flaking.

10.   This process inevitably makes each hair shaft slightly rougher, drier and more vulnerable.