Saturday, September 30, 2023

Why does hair curl in summer?

We republish this article by Tena S. Carpenter, Professor of General Chemistry at the University of Maryland, Baltimore County, published in The Conversation on August 17, 2023.

If you have curly hair, you know that every day is a new adventure. What will my hair do today? Why does it curl better some days than others? Even the smartest of hair can find it frizzy—or, let’s face it, frizzy—on humid summer days.

As a person with curly hair, I am always looking for the best way to care for and understand it. As a chemist, I am interested in the science behind the behavior of my hair at the molecular level. There is different types of hair, from straight to curly, and behave differently depending on their structure. But the molecular composition of the hair is the same.

hair structure

hair starts to grow beneath the skin’s surface, but it’s what happens after it breaks through that determines whether you’re having a good hair day or a bad one.

Each hair can have three hats: the medulla, the cortex or cortex and the cuticle. It is as if each hair was a small tree trunk.

The core of the hair is the marrow. retains moistureas the marrow in the center of a tree trunk. It is also a very fragile part, but only thick or rough hair contains it. People with fine or blonde hair normally They do not have a medullary layer.

Below is the Cortexwhich constitutes the bulk of hair and is analogous to the wood of a tree. The cortex is made up of spring-shaped protein molecules that are arranged in parallel rows in a cylindrical bundle. The exact shape of that beam is determined by the hair follicle, which is a pore of the skin from which hair grows.

The way the hair exits the follicle influences the distribution of its proteins. So, a straight follicle produces straight hair and a curved follicle produces curly hair. The less evenly distributed the proteins, the curlier the hair will be. The genetic code also influences the shape of the bark and therefore the shape and thickness of the hair.

Finally, the outermost layer of the hair is called cuticle. The cuticle is like the bark of a tree, and even looks like bark under a microscope.

The function of the cuticle is protect the barkbut the cuticle is damages very easily. Imagine lifting or removing the bark from a tree. Doing so will expose the interior wood to moisture loss, the environment, and deterioration.

The same goes for each hair. When the cuticle is damaged by brushing, chemicals, wind or heat, the cortex proteins they have a much harder time sticking together. This means they can lose moisture, gain it, fray like rope—causing split ends—and even break. All these factors can influence the appearance of the hair.

hair in summer

And what does all this have to do with humidity? Well, hair proteins contain many permanent chemical bonds. Only chemical treatments such as perms or straightening can change these bonds. But there is another natural phenomenon that keeps the protein molecules in the cortex in line: something called hydrogen bond.

The long, stringy protein molecules in the bark contain tiny positive and negative charges throughout its structure. as opposite charges they attractentire rows of proteins can be attracted to each other like weak little magnets.

Heating or wetting the hair breaks the magnetic attraction between these protein rows.. Thus, heat and water can reorganize hair proteins breaking hydrogen bonds that hold its structure together.

Water is one of the best hydrogen bonding molecules. So when a water molecule has a chance to form a hydrogen bond with something, it does.

In hair, water can form hydrogen bonds. between protein rows in the capillary cortex. It is the degree to which this occurs that determines the fate of the hair.

When only a little water gets into the hair, as can happen in low humidity conditions o When the cuticle is healthy and able to keep a lot of water out of the cortex, the hair can curl. When the humidity is high or the cuticle is damaged, more water enters the hair. Too much water can swell and crack the cuticle, causing it to hair looks frizzy.

Many people consider the problem with frizzy hair to be humidity, but styling in a humid environment and then moving into a drier one can also be a problem. The water molecules that leave the capillary cortex can also cause a change in the behavior of the hair.

treat hair in summer

A damaged cuticle layer leaves the cortex more susceptible for water molecules to get in or out and wreak havoc on your hair. Every time water molecules enter or exit, the structure of the hair suffers and the style can be ruined. When the cuticle is healthy, it can protect the cortex and make the hair is less susceptible to climatic or environmental changes. In summary, a healthy hair cuticle helps maintain adequate moisture in the cortex.

Heat from styling tools is the biggest culprit in damaging cuticles, but chemical treatments, brushing, sun and wind can also cause damages. Avoiding these activities can help, but some things, like sun exposure, can’t be avoided.

You can also take care of your scalp: a clean and healthy scalp leads to healthy hair cuticles. Using moisturizing products on your hair can also help maintain cuticle health. Oils and moisturizing treatments can even restore damaged cuticles. The good news is that if you know your hair well and treat it well, you can help prevent the unwanted effects of humidity.

The Conversation


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