Curly hair is determined by the shape of the hair follicle, controlled by a gene. Curly hair differs from straight hair in structure, chemistry, and oiliness. The shape of the follicle influences the formation of disulfide bonds, which cause curvature. The origins of different hair types are unclear. Changing hair type is possible but temporary. Curly hair requires different care than straight hair to maintain its natural health.
Numerous theories have been put forward as to why some people have curly hair and others straight. For many years this was believed to be determined by the shape of the hair shafts: those with a round cross-section were straight, those with an oval shape were wavy, and those with a flat profile were curly. Another theory was that in curly hair, one side grows faster than the other, causing it to curl. Scientists currently think that type is largely determined by the shape of the hair follicle, which appears to be controlled by a gene.
The structure and chemistry of hair
Curly hair is known to differ from straight hair in many ways other than shape. It is extremely rare to find someone with both curly and oily hair. Biologically, this makes sense, because the oils secreted by the follicle’s sebaceous glands can travel more easily along a straight shaft. Anyone with this type of hair knows that it can be dry, difficult to manage, and often frizzy. The good news is that split ends are less common.
Another difference, on a chemical level, is in the structure of the proteins that make up the hair. It consists mainly of a protein called keratin, the same material that makes up skin and nails, and molecules of this compound join together to form fibers. The protein molecule contains sulfur atoms which can sometimes bond with each other, forming what is called a disulfide bond. When these form between atoms far enough apart, it causes curvature. The more disulfide bonds there are, the curlier the hair will be.
The influence of the shape of the follicle
Hair grows from tiny tube-shaped cavities in the skin known as follicles. People with curly hair appear to have a hooked, rather than straight, shape of the follicle. This shape is thought to push the parts of the keratin molecules containing sulfur atoms closer together, making it more likely that disulfide bonds will form.
The origins of the different types
Naturally curly hair is genetically determined. Some genes are said to be dominant over others; this means that when an individual inherits two different genes for the same trait, one is more likely to be expressed than the other. For example, the gene for long eyelashes is dominant over the gene for short eyelashes, so if someone inherits one from their parents, they will have long eyelashes. The non-dominant gene is said to be recessive and will only be seen if it is inherited from both parents. The gene for curly hair is said to have incomplete dominance over the gene for straight hair, so an individual who inherits one straight and one curly gene may have intermediate and wavy hair.
It is unclear why these different types evolved. It has been theorized that as early humans spread from Africa into colder, cloudier regions, straight hair evolved to offer greater protection from the cold, at the expense of increased exposure to ultraviolet light. Some experimenters have claimed that curly hair offers better protection against ultraviolet rays, while straight hair captures air better near the scalp, providing an insulating layer for a part of the body that would otherwise be very prone to heat loss. However, there doesn’t seem to be any consensus on this.
Change your hair type
Not all curly hair is naturally like this. Many people choose to change their type by applying various treatments. One method is to wrap hair around rollers while wet. This causes hydrogen bonds to form between the keratin molecules, resulting in a curved shape which depends on the size of the rollers. The hydrogen bonds, however, are much weaker than the permanent disulfide bonds that cause natural curls, and the effect is lost when the hair gets wet again.
Chemical methods can be used to create disulphide bonds in straight hair, giving a longer lasting effect, but the new growth will be straight, so again, the effect will eventually be lost. Scientists are looking for ways to change the shape of the follicle to achieve a permanent effect. It’s about studying in detail how the curly hair gene works, which is still an active area of research.
Treatment
The biggest challenges for most people with this type of facial hair are dryness and unmanageability. Because many use chemicals and heat, the dryness tends to get worse. Curly hair requires different care than straight hair to maintain its natural health. It doesn’t require washing every day and will benefit from an occasional break from chemicals and heat. Whenever it is washed, it should be deeply conditioned and, if dry, alcohol-containing styling products should be avoided. Proper attention to hair care will improve its overall health and manageability.
Protect your devices with Threat Protection by NordVPN
