Why Does Humidity Make Your Hair Frizz?

Humidity makes hair frizz because hair is hygroscopic: it pulls water from the air. The water molecules slip in and let the weak hydrogen bonds between the hair’s keratin proteins break and reform in new positions. The strands swell, the cuticle lifts, and the keratin folds back on itself, so the hair puffs up and frizzes.

Frizzy hair is what you get when thirsty, dry hair soaks up moisture straight out of the air. That water sneaks into the protein structure of each strand, makes it bulge and lift past the cuticle, and leaves you with a wild, frizzy mane.

For many people in the world, walking outside on a humid day is more than just uncomfortable; it can also wreak havoc on their hair. The battle to overcome frizzy hair is ongoing and seemingly impossible to win, particularly for people with dry or naturally curly hair. The question is, why do humid conditions cause your hair to take on a life of its own? And why do some people seem immune to this unsightly and annoying situation?

The Science Of Hair Strands

While a strand of hair may seem incredibly thin to the human eye, when seen under a microscope, there are many different layers and rings, almost like the rings around a tree. The outer layer is known as the cuticle. At the very center sits a thin core called the medulla, which is small and often missing altogether in fine hair. The layer that does the heavy lifting, though, is the one in between: the cortex. It makes up roughly 90 percent of the strand by volume, and it is packed with keratin proteins.

These keratin proteins form long bundles and attach to one another in various ways to maintain the shape and integrity of your hair. The way they attach, however, is not always the same, which is where this story gets interesting. Some of the proteins form a disulfide bond, which is when two sulfur atoms form a covalent bond. This is quite a strong bond, and will provide strength to your hair.

However, the second common bond between these proteins is a hydrogen bond, which is much weaker, and far more prone to breaking. Basically, whenever your hair gets wet and then dries, new hydrogen bonds are formed in your hair, millions of different weak bonds that could easily get broken by the next splash of water or rainstorm.

As your hair dries, it tends to stay in basically the same shape as when it was wet, which is a good thing, until you walk outside on a humid day. Since there is so much moisture in the air when it is humid, dry hair starts soaking up those water molecules as quickly as it can. Each water molecule can bridge two neighboring keratin chains, so countless new hydrogen bonds form, pulling the keratin proteins in the cortex to fold over on themselves. This makes the strand swell, lifts the cuticle scales on the surface, and on the large-scale visual level means that previously straight strands of protein become bent and twisted. The strong disulfide bonds stay put through all of this (only chemical treatments like perms can break those), which is exactly why the effect is temporary and your hair springs back once the air dries out.

The result of this over-saturation of water in the air, in combination with dry strands of proteins eager to attach to water molecules, is frizzy hair!

This also explains why naturally curly hair frizzes the most. The cortex of a curly strand is built unevenly: one type of cortical cell (the orthocortex) sits along the outer curve, and a denser type (the paracortex) sits along the inner curve. These two sides drink up water at different rates and swell by different amounts, so on a humid day each strand twists harder and lifts away from its neighbors. Straight hair, with the two cell types spread evenly around the strand, swells more symmetrically and frizzes less.

How To Avoid Frizzy Hair

The best thing about understanding science is making it work for you, and when it comes to frizzy hair, there are a few excellent ways to avoid those bad hair days. First of all, frizzy hair is experienced primarily by those with dry hair, as well as those who use a lot of products or undergo hair treatments.

Given that knowledge, one of the best approaches to avoid frizzy hair is to ensure that your hair is well moisturized. Basically, if your hair is already creating ample hydrogen bonds, humidity won’t be able to affect the shape of your hair very much. If your proteins are already saturated with moisture, there is less room for extra water to rush in, so they swell less and the cuticle stays flatter.

People who have bleached, dyed and crisped their hair to an unhealthy state will also be prone to frizzing, as the basic structure of your hair strands may already be compromised, making it easier for things like split ends and frizz. If you overuse shampoo, brush your hair too hard, overheat your hair or regularly get perms, your hair is highly likely to be dry.

The best option for most people is using conditioner more regularly, even instead of shampoo in some showers. The natural oils in your hair will then be allowed to build up, which can also prevent frizzy hair. Applying natural oils like coconut oil and other herbal solutions is also an effective way to increase moisturization of not only your hair, but also your scalp.

Ensuring proper nutrient delivery to every part of the hair will help prevent weakness and breakage, and make you less susceptible to having an exploding puff of hair by the end of a hot summer’s day.