The shape of hairs as they grow is determined by genetics, so if one of your parents has curly hair, you’re likely to as well.
Your genetics affect the shape of your hair follicle, which it turn affects the angle of hair growth from the scalp which will result in a spectrum of shapes from super sleek and straight to a majestic zig zag. As the hair grows out of the follicle proteins in the cortex will bond and this keeps your hair shape in place from root to tip.
Everyone has a unique hair shape and not every hair follicle on your head will be the same, some might be straighter and some might be curlier. However there are four points along the spectrum of hair shapes, from the straightest to the most zig zagged afro hair that are useful beacons from which you can determine how your hair will behave and how to maintain it.
Knowing your overall hair shape will boost a successful maintenance routine and allow you to address the needs of the hair and scalp.
Straight hair reflects the most, appearing shiny and is the most resilient hair of all of the hair types. The cross section would appear round. It is hardest to damage but can also be difficult to hold a style or curl this hair texture. Sebum easily spreads from the scalp to the ends without anything to interrupt its path, people with straight hair may find their scalp and hair accumulates sebum easily and can be hard to achieve volume with without the right ingredients from the start to finish of your hair care.
Wavy hair can often appear straight at the scalp and curlier at the ends giving gentle movement and body. This is because gravity and the weight of the hair is pulling the hair straight at the roots, whereas the ends show how wavy the hair actually is. Sebum will find it easy to travel down the straighter hair near the roots but less so down the curlier ends. Hair can appear shinier and more resilient to damage near the roots and may be drier and more prone to damage near the ends. This more porus hair can be more fragile and prone to breakage, especially when wet and during combing and styling. In humid environments, the hair can absorb water and swell, becoming frizzy or fluffy.
Curly hair gives tumbling bounce and movement. The hair has even more curve to it, which means there is a less straightforward way for the sebum to travel down to the ends of the hair. This means the hair can be more prone to breakage and dryness.
Coily hair is much more curvy, and the cross section looks like a jelly bean. This hair curls more tightly or can zigzag. It can hold wonderful styles with great volume, although may be fragile and prone to breakage. This hair may need lots of moisture to keep it pliable and conditioned. Specific combs and brushes can limit breakage and will be easier to comb through when the hair is wet. Coily hair can be quite difficult to straight and may equire a chemical treatment like a relaxer to get the desired look.
The shape of the hair has nothing to do with fine versus thick. Fine and thick refers to the diameter of each hair itself, while thick and thin refers to the number of hairs on your head. You can have thick, fine hair that can be straight or curly.
In practice if two people want a volumising effect on the hair and one person has natural wavy hair, and the other person has naturally straight hair the person with naturally straight hair will require more vigorous volumising formulas. Each step of the routine should contain a volumising effect.
Wavy hair would require less overall styling, it can naturally achieve more volume at the ends, so focus the volumising effect on the roots and add some light conditioning to protect them from breakage.