Bad hair day? Blame this warm, humid weather

Woman with frizzy hair (Getty Images)

Ladies (and longer-haired gentlemen): Do you feel like your hair is waging war against your head?

Been styling it and trying to tame it to submission, but it still comes out looking frizzy?

You can blame the weather — specifically the warm, humid, summer-like conditions we’ve been experiencing lately in the Tennessee Valley.

The battle of the frizz: Why humidity plays a role

Believe it or not, hair changes length based on the amount of water vapor that is present in the air. The drier the air, the shorter the hair shaft; the more humid the air, the longer the hair — and the more frizzy/curly it becomes (this length can change as much as 2.5 percent of the overall length of the hair shaft, according to the Belfort Instrument company). In fact, human hair is often used within hygrometers (instruments that measure the moisture content in the atmosphere) due to this principle.

Cross section of a strand of hair (Image: WHNT News 19)

But why does stretching/shrinking situation happen, and what is the weather’s role in the size change?

Consider the structure of a single strand of hair. The outer shell consists of several flattened layers that make up the cuticle. The cuticle surrounds a matrix of cortical cells (known as the cortex), which in turn surround the central core of cells, known as the medulla.

HeadOfHair.com explains that when the layers within the cuticle are intact and closely folded together (like shingles on a roof), the result is a glossy, shiny look to the hair. However, in the case of damaged hair — or when the humidity is high — the layers of the cuticle will unfold and fray, exposing the cortex.

Natural hair pigments or hair dye is located in the cortex, which consists of a protein called keratin. Keratin is a type of protein that consists of polypeptide chains that are themselves long and coiled, and those coils are held together by two different types of bonds, one of which can be easily disrupted by water vapor present in the air.

Peptides within the hair cortex. (Image: WHNT News 19)

During high humidity, the amount of water vapor in the atmosphere increases, which means the number of hydrogen molecules present in the air increases. ScientificAmerican.com explains that these extra hydrogen molecules bind to the keratin within the hair cortex, preventing the hair strands from binding with each other. The result is a lengthening — and spiraling — of the hair, causing the frizzy, overly curly hair days that happen so frequently in the spring and summer.

Frizzy hair sufferers, know that you aren’t alone! Below is an example of my normally frizzy hair. Sometimes I flatten it with a curling iron, other times I go with the flow and embrace the waves.