The shape of your hair follicle helps determine the curvature of your strands, says Kingsley. Ovals yield curly hair and circles produce straight hair. That means an individual strand won't start straight and then become curly—but because the midlengths to ends are the oldest parts of your hair, they've been subjected to the most damage, which can make them unruly and wavy. Plus, the shape of your follicles can vary at different spots on your head, says consultant cosmetic chemist Mort Westman.
Wash: Torn between the products for wavy or curly hair and the ones for straight and sleek? "Pick formulas based on your hair's needs, like hydration or shine, rather than the style you want to achieve," says Wilkerson. And you're not locked into matching your shampoo and conditioner. "A volumizing shampoo, for example, will remove dirt and oil without being too heavy on straight strands, but a more moisturizing conditioner can help your wavier sections, which tend to be drier." To avoid weighing down your roots, apply conditioner from just the midlengths to ends, then run a comb through your hair to ensure every strand is coated before rinsing.
Treat: Once or twice a week, add a moisturizing mask to your cleansing routine.
John Masters Organics Hair Mask for Normal Hair, $29; JohnMasters.com
Style: Want to go wavy all over? Apply an antifrizz spray (for fine hair) or cream (for thick hair), and layer a curl-enhancing cream on top. Wrap one-inch sections of hair around your fingers, and secure the twists with pin curl clips. Once hair is almost dry, remove the clips. If you'd rather play it straight, apply a lightweight, heat-protective antifrizz spray or cream, then massage a dollop of volumizing mousse into your roots. Using a round ceramic brush, blow-dry your hair. "The heat from a dryer is less direct and intense than a flatiron, so it's not as damaging," says New York City hairstylist Lisa Chiccine.
Garnier Fructis Sleek & Shine Zero Smoothing Light Spray, $6; drugstores.
