Why is hair curly underneath and straight at top?

Hair is an interesting topic in which people are very interested in finding out about. But every time you hear about the reason behind something, it always seems to be very complicated. But when it came to my attention about why hair is curly underneath and straight at the top, the cause turned out to be very simple, we have curly hair underneath and straight hair atop.

And if you are lucky enough to have straight hair then you should be thankful for it. Curly hair is not that easy to deal with, especially if it is somewhere at the back of your head. You can’t just straighten it out and need to use a lot of styling products to keep your hair tame and looking good.

Structure of Hair on different parts of the body

Curly hair is a genetic trait. Hair on different parts of the body have different structure and therefore behave differently. Hair is composed of a protein called keratin which is a fibrous protein. Hair is also a dead tissue and so doesn’t have a blood supply to nourish it.

The question of “Why is hair curly underneath and straight at top?” often comes to mind when you notice the patterns on the head of a human being. It is no surprise that a lot of people have a strong reason for why this is happening. 

Hair on the head of a human is naturally curly at the bottom and straighter at the top. This is called hair texture. Hair texture is dependent on how much curl the hair has on the hair strand. Curls create the hair structure of the hair strand and this is different for every strand of hair on the head of a human.

Why does hair become curly or underside?

Hair becomes curly on the underside because the hair strands are very fragile. They are fragile because they are more tightly wound. When you curl hair under it is to make it look thicker by exposing the underside of the hair.

As hair grows, the tip of the hair is exposed to the air, which dries out the hair. The upper layers of the hair curl inwards to protect it from dryness. The curly tip is not only the oldest part of the hair, but also the weakest. Eventually, when the tip falls out, it leads to baldness.

Unless you are referring to hair of a specific race, generally hair is curly on the bottom because this is where an individual’s follicle is strongest. The hair shaft is composed of three layers; the cuticle, the cortex, and the medulla. The cuticle is the outer layer of the hair shaft, and is the portion that is frequently seen.

The cuticle is made up of many layers of keratin that are tightly packed, forming a hard structure that protects the cortex beneath. The cuticle scales overlap, so they form the outer edge of the hair shaft. The cortex of the hair has the pigment cells, which determine the color of the hair. The cortex is the middle part of the hair shaft, and makes up about 90% of the follicle. The medulla is the innermost portion of the hair shaft, and is made up of air chambers that help with the circulation of air in the hair.

Knowing more about hair and its strands

Every strand of hair is made up of keratin, just like your fingernails. And like your fingernails, they start out straight and then curl up at the end. The difference is that the top of the strand is flat, not rounded like the bottom. This is because the bottom of the strand grows at the same rate as the rest of the strand. But the top of the strand, due to gravity, is pulled by the weight of the hair on top of it. 

The more of the strand that is on top of it, the more of the bottom of the strand is pulled down. So more of the bottom of the strand is pulled down, the more of the bottom of the strand grows out of the skin, and the curvier the hair becomes.

Whenever you see your hair straight it’s actually “relaxed”. That means, your hair is springy and elastic, so it’s always trying to curl up. Whenever you see your hair curly it’s always relaxed. The reason for this is that the hair is made up of many layers of cylindrical cells. Whenever the hair is growing, the cells are filled with water.

They are springy and stretched out. If the hair is straight, then the cells are stretched out evenly, so the hair looks straight. If the hair is curly, then the water is not evenly distributed throughout the cells, so the hair kinks.

Hair goes through different growth cycles. During the anagen phase, the growth phase, the cells in the inner layer of the hair follicle divide rapidly and the hair pushes upward and outward. The outer root sheath, which is made up of keratin, the same protein as our skin, separates from the dermal papilla, which is responsible for keeping the hair pigment and nourished.

The outer root sheath begins to curl and coil as cell division, migration and differentiation take place.  Any number of things can cause unusual texture in the hair: over-processing, over-styling and environmental factors. While much of this coiling and curling can occur naturally, some hair may be prone to this type of texture. 

Hair that is curly or tightly coiled tends to be more fragile. This often leads to hair breakage, hair loss, hair thinning and hair that is easily tangled. Understanding hair texture can help you achieve healthy hair.

At the bottom of each hair is a tiny club-shaped structure called the hair follicle. The hair that is touching the scalp is attached to this follicle. As it grows, the hair follicle begins to curve like a hook and the longer it gets, the more the curl becomes visible. This is because the hair above the scalp is growing straight out of the follicle.

According to studies, the main reason for this is because the hair at the roots is under the most stress and therefore the most likely place to be damaged. The ends of the hair are free from the most stress and therefore the least likely to be damaged.

A secondary reason is because curly hair is naturally drier than straight hair. The drier the hair, the more likely it is to break. Therefore, the ends of the curly hair are more likely to break off and therefore straighten out.