As each strand of hair grows, it moves through three development stages: anagen, catagen, and telogen. The anagen stage is your hair's growth period, which typically lasts from 3 to 5 years. At the end of the growth period, the follicle prepares for a rest. The transition period - which typically lasts a month - is called the catagen stage. During this stage, the strand is still secure in the follicle but the lower portion of the follicle collapses. The telogen stage, the resting period, lasts for about 3 to 4 months. At the end of the resting stage, the hair falls from the follicle, a new hair begins to grow, and a new anagen phase begins.

Hair grows about one half-inch (1.2 cm) per month. A normal healthy hair is as strong as copper wire of the same diameter.

Straight or curly

I should also mention that your hair's curl pattern - or lack thereof - is formed deep in the follicle. Here, at the hair's roots, your strands are soft and pliable, adapting themselves to the shape of the surrounding hair follicles. If your follicles are genetically round, they'll create straight hairs; slightly oval follicles produce wavy hair; and flat-oval follicles produce curly hair. Study a cross-section of a straight strand, and you'll see the hair's round shape; study a cross-section of wavy hair, and you'll notice the oval shape; if you cut across a curly strand, you'll see the hair's ovoid shape.

What does all this have to do with curls? A circular cross-section of hair - or yarn, or string, or wire - boasts equal strength in all directions across the fiber. Because this shape features no weaker areas, hair hangs rigidly without coiling in on itself. As with all wirelike entities, an oval or flat-oval cross-section of hair is strongest across the wide part of the cross-section and weakest across the narrow cross­section. Weaker areas aren't rigid like strong areas. Instead, they are flexible and likely to twist around. This means wavy or curly hair boasts enough flexibility through its narrow cross-section to encourage strands to flex (wavy hair) or coil (curly hair).

As the wavy-haired daughter of a straight-haired mother, I feel obliged to offer this advice: Do not make your curly-haired child feel self­conscious about her hair! This can damage her confidence and lead to later abuse of blow-dryers and straighteners. Do not continually ask your child if she has brushed her hair - no amount of brushing is going to make curly hair smooth and it can make it even messier!