And wavy hair wavy? Well, as you may have suspected, it does have to do with genetics, but other factors influence hair growth as well. According to Proctor and Gamble, researchers do not completely understand why some hair twists and turns and some lays flat, but here are the most commonly accepted theories. Some are a little more scientific and others more commonsense.
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  • Shape and opening of the follicle: If you have curly hair, your follicle is probably very flat in diameter. Straight-haired people have circular follicles. As for the wavy bunch? They have oval-shaped follicles.
  • The number of twists per unit length: Even the straightest of hair twists as it grows. The more twists, the more curl.
  • Humidity in the air: Hair, which is porous by nature, easily absorbs moisture molecules in the air, making the hair curl or frizz. Enough said.
  • Hormones and medication: Changes to the shape of the follicle caused by hormones and medication can alter the texture of your hair and the way it grows.
  • The position of the hair bulb in the follicle: The bulb is located at the bottom of the hair shaft. People with really curly hair may have a hooked end towards the bottom of the shaft, meaning their hair grows at more of an angle. Straight hair means little to no hook.
  • The number of disulfide bonds in the hair: Simply put, the way protein structures are arranged in each hair shaft effect how hair behaves. The more disulfide bonds that occur between hair proteins, the curlier the hair and vice versa. This explains why you can temporarily alter the texture of your hair with heat and/or water — just by breaking bonds.