Back in the day, folks believed that the shape of a person’s hair was determined by the individual hair shafts; that curly hair was curly because the hair shaft was flatter and had more intertwined layers than straight hair, which was round. Then, the folks at L’Oreal Paris found that it wasn't the shape of the hair shaft, but the shape of the hair follicle, and that the shape of the hair shaft simply follows suit.

Now we know that curly hair biologically different than straight hair. It is extremely rare to find someone with hair that is both curly and oily. Biologically, this makes sense, because the oils secreted into the hair shaft by the sebaceous glands can more easily travel down the shaft of straight hair. Anyone with curly hair knows that this hair type can be dry, hard to manage, and often frizzy. The good news is that people with curly hair tend to have fewer split ends than people with straight hair.

The amount of curl in curly hair is also dependent on the shape of the hair follicle and shaft. The hair follicle below the scalp has a hooked end in people with curly hair. The more hook the follicle has, the curlier the hair is. Those with straight hair have hair follicles with no hooks.

While scientists are studying the impact of drugs that can change the shape of the hair follicle, those who simply wish to experiment with a different hair type have many options besides resorting to medication. The shape of hair can be changed chemically, which offers a permanent change until new hair grows out. The shape of hair can also be changed thermally with curling or flat irons, which provides a temporary change lasting until the hair is washed.

The biggest challenges most people with curly hair face are dryness and unmanageability. Because many people with curly hair abuse their hair with chemical and thermal products, the dryness tends to become worse. Curly hair requires different care than straight hair in order for it to maintain its natural health. Curly hair does not require washing everyday and will benefit greatly from a low-poo or no-poo routine.  Drug store shampoos and conditioners often contain ingredients that are very damaging to curly hair. 

Curly hair tends to be more fragile that straight hair.  As such, it needs protection from sun, salt, chlorine, harsh chemicals (relaxers, texturizers, perms, bleaches), and from heat. 

Curly hair should be handled with care.  Unless you are using a denman brush, throw out your hair brush.  Brushing curly hair actually causes breakage.  Use your fingers.  Use a wide toothe comb.  But get rid of that brush.  Even the denman brush must be used carefully - curl by curl.  It should be washed gently, only detangled while thoroughly saturated with a high slip conditioner, and detangled carefully, working from the ends up toward the scalp.  It should be deep conditioned at least one a week.  Avoid styling products that contain alcohol and silicones. Proper attention to hair care will improve the over all health and manageability of curly hair.