Any time big words start getting thrown around, people are bound to get confused. We’re here to cut through the chaff and address one such word, which represents the chemical responsible for about 90% of your hair’s strength: cysteine.
But first, some background...
What is Hair?
Hair - like skin, nails, fur, feathers, and pretty much any other exterior biological surface - is partially composed of a protein known as keratin.
Keratin is physically durable and chemically stable. These two properties make it ideal for absorbing the physical rigors of life on Earth and protecting the more delicate tissues that lie beneath.
These “physical rigors” include water, wind, and abrasive substances like sand... which all seem relatively harmless precisely because we have keratin in our skin and hair that protects us from the damage that can be caused by wetness and abrasion.
But hair isn’t indestructible, and proper care should be taken to ensure that your hair is healthy, well-nourished, and ready to take on the world (or at least a humid day at the beach).
What is Hair Made Of?
A strand of hair is born in a hair follicle which is a small opening in the surface of the skin from which hair, sweat, and sebum (the oil that coats our skin and hair) escape. At the base of a follicle is a grouping of cells known as the dermal papilla. This structure continually produces new hair cells, pushing older ones up and out of the follicle, where they die and harden.
The dermal papilla forms hair in two (sometimes three) layers: an exterior protective cuticle, and an interior structural cortex just beneath the cuticle. Some coarse hairs also have a medulla beneath the cortex, adding rigidity but not affecting health, color, or texture.
The cortex of a hair strand consists primarily of keratin, melanin, and water. The type and amount of melanin determine hair color while keratin provides strength, elasticity, and texture. Water enhances the elasticity of keratin; split ends occur when the cuticle is damaged allowing water to evaporate from the cortex below. This dryness causes the keratin fibers to fray like the fibers of a rope, and a lack of cuticle allows the fray to spread and become visible.
The cuticle is formed by flat, overlapping cells which lock moisture into the cortex and keep it structurally intact. Cuticle cells are transparent yet smooth which gives hair its characteristic appearance: transparency allows most light to pass through the cuticle and interact with melanin in the cortex giving hair its color; surface smoothness reflects some angular light, giving hair its silky shine. Hair repair efforts focus primarily on the cuticle.
Keratin, a protein produced by almost all forms of life, is integral to both the cuticle and the cortex of our hair. Keratin in one form gives the cuticle its strength and resistance to abrasion while in another form, provides the cortex with its strength and elasticity.
But what gives keratin its strength and elasticity? I’m glad you asked…
Cysteine: Strong and Stylish
Cysteine is an amino acid. Amino acids are like Lego pieces allowing them to form long chains with one another known as polypeptides even though the individual building blocks aren’t all the same. In a polypeptide, each amino acid is known as a residue. Because there are 20 different amino acids, polypeptides containing different amino acid residues will have different characteristics. Thanks to these differences, some polypeptides can join with each other forming proteins (just like amino acids join with each other to form polypeptides).
Proteins are large molecules produced by all forms of life that perform extremely numerous and diverse functions from the contraction of muscle cells (myosin) to the perception of different colors of light (rhodopsin), and everything in between including comprising the physical characteristics of hair. All protein functions are determined by the unique order of amino acid residues that comprise that specific protein, just like the same lego pieces can be combined in different orders to create different designs.
Cysteine contains a highly reactive sulfur atom, which is its most blaring characteristic. When polypeptides are forming, the sulfur atoms of two adjacent cysteine residues will bind with one another in what’s known as a disulfide bridge. Disulfide bridges are present in every single protein, and they’re responsible for the overall shape, therefore overall function, of a given protein.
The protein keratin contains about 17% cysteine, but the placement of these residues in the polypeptide chain gives keratin a structure that is similar to steel cable: a type-1 keratin alpha-helix (which is acidic) will coil around a type-2 alpha helix (which is basic), creating a dimer consisting of a double helix (similar to the structure of DNA). These dimers then link with one another forming protofibrils, which in turn bind together forming intermediate filaments.
There are millions of disulfide bridges in each intermediate filament, thousands of these filaments in each hair cell, and millions of hair cells in each strand of hair. The sheer number, as well as strength, of these disulfide bridges, accounts for about 90% of the tensile strength of a strand of hair. By weight, hair is stronger than steel, and it’s all thanks to disulfide bridges formed between cysteine residues in keratin.
So What Does This Have to do With My Hair Routine?
There are many steps to take if you want beautiful, healthy, voluminous hair, but a cysteine hair repair treatment may be too little too late…
Hair is “alive” - with access to nutrients like cysteine - only when it’s still in the follicle. As the follicle produces new hair cells below the older ones, the strand is pushed upward, which kills and hardens the older hair cells. The composition of hair as it leaves the follicle is its final composition, and it can no longer be changed or modified by treatments or supplements.
However, steps can be taken to strengthen and protect the hair strand even after it’s no longer receiving nutrients from your blood supply. The most important aspect of hair repair treatments and products is their pH level.
Human hair - as well as the keratin which gives it substance and durability - is very sensitive to changes in pH. On average, the pH of our hair is about 5.5-6.5: slightly acidic. An acidic environment protects the disulfide bridges that give keratin its strength. Mild acidity also tightens and hardens the cuticle as a whole; partly through fortification of cuticular keratin, and partly through strengthening the bonds between cuticle and cortex.
On the other hand, basic conditions with a pH greater than 7 can soften the cuticle and make it porous, weakening the oh-so-precious disulfide bridges that give strength and bounce to your hair.
Whether your ends are split, or you have dry, damaged hair, repair it by switching from bargain brand hair products to pH balanced, nutrient-rich products designed specifically to keep your hair smooth, healthy, and free from microscopic damage that leads to split ends and worse, greying.
You can boost your hair’s health and beauty at the same time, with pH balanced hair care products, like Salon pHactor!