I’m a chemist and I’ll explain why your hair gets frizzy in the summer

Curly hair and moisture: the science behind the glamorous secret of unruly hair

Who has curly hair, knows well that every day is a surprise: will they be soft and defined, or curly and rebellious? And why does it change so much based on weather and humidity? The teacher answered these questions Tara S. Carpenterprofessor of chemistry and biochemistry at the University of Marylandin USA:

There are different types of hair, from straight to curly, and they behave differently depending on their texture. But the composition of the hair at the molecular level is the same.

Each hair can have three layers: pith, cortex and cuticle. You can imagine each hair as a small tree trunk. The innermost layer, or core, is the medulla. This holds moisture, just like the pith in the center of the tree trunk.

Then there’s the bark, which makes up most of the hair and is analogous to the wood of a tree: It’s made up of spring-shaped protein molecules that are arranged in parallel rows in a cylindrical bundle. The exact shape of this bundle is determined by the hair follicle, which is the pore in the skin from which the hair grows.

The way the hair leaves the follicle affects 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. The genetic code also plays a role in the shape of the cortex and thus the shape and thickness of the hair.

Finally, the outer layer of the hair is called the cuticle. It’s like tree bark (and even looks like bark under a microscope).

The hair cuticle is also the most vulnerable part of our hair because – being the most exposed – it can be easily damaged by the use of aggressive products, heat or brushing too intensively. Similar inconveniences can change the structure of the hair: in practice, the proteins of the cortex can be difficult to release against each other, which leads to the accumulation of more or less moisture or to breakage of the hair. This brings us to the big question: why does hair frizz in humidity?

Hydrogen bonding

The protein molecules of the bark are held together by a natural phenomenon called “hydrogen bonding“. These molecules have tiny positive and negative charges throughout their structure. When confronted with opposite charges, they attract each other like little magnets. Heat and humidity can stop this type of attraction and “break” the hydrogen bonds that hold this structure together.

When too little water enters the hair shaft, which occurs in low humidity conditions or when the cuticle is healthy and able to retain excess water from the cortex, the hair can become frizzy. With high humidity or damage to the cuticle, more water enters the hair. Excess moisture can swell and break the cuticle, making hair look frizzy.

But Professor Carpenter was keen to point out that hair doesn’t just curl from humidity, but from use hair products and tools can significantly affect the shape of your hair:

Heat from styling tools is the most common culprit for cuticle damage, but chemical treatments, brushing, sun and wind can also cause damage. Avoiding these activities can help, but some things, such as exposure to the sun, cannot be avoided.

How to avoid this inconvenience? Simple: enough take care of your hair through use moisturizing products such as oils and masks that can help restore damaged cuticles.

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Source: University of Maryland, Baltimore County

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