Recently I was contacted by a pal who is currently working on an Education Program for Hairdressers in his part of the world. We had an interesting conversation and a bit of a debate about the importance of the different bonds in the hair. It’s a subject that has resurfaced in the last decade along with the growth of plex/bond-builders. With our conversation still ringing in my ears I decided to captured some bond insights here in this blog. Geek alert on this one!
As professionals we learn there are two main groups of bonds giving our hair its structure 1) Permanent Bonds, and 2) Temporary bonds. Admittedly I don’t like the terms permanent and temporary as they imply a level of importance that is not an accurate representation outside the world of chemistry. No matter the type of bond they are as a result of Amino Acids the building blocks of hair and nails as well as many other parts of our bodies.
Polypeptide 
Amino Acids; There are around 20 in our hair, each can link up through peptide bonds to form chains (polypeptides) that fold up into functional proteins, as well as unique side chains, think charms on a charm bracelet. Spiralling intertwined Peptide chains are held together by series of paired bonds one such paring is Disulphide Bond. The other charms are still involved in charm-charm interactions, the difference with the Disulphide Bond is that it is a covalent bond, (it’s a chemistry thing) so it’s strong and splitting and unsplitting involves reduction and oxidation reactions.
Permanent Bonds; hair has a lot of cysteine and cystine and is a major individual contributor to the make-up of our hair. Inside each strand of hair there are actually lots of strands of the protein KERATIN. The protein KERATIN gives our hair and nails their strength from the disulphide crosslinks holding the strands of keratin together. Each strand has lots of Cysteine, so lots of ways to link and the choice of way influences the curviness of our hair. Keratin is stretchy, so we can force our hair into different shapes but it will de-bounce back unless we use some chemical force.
In a perm or straightening, we physically force hair into the shape we want (e.g., curl it around curlers or straighten it through combing or ironing). During a texture service we apply a reducing agent to reduce the crosslinks to allow the hair to stabilize into new positions and then add an oxidizing agent to make new cross-links in the new position. Ta-dah new waves or straightened hair permanently… well at least until it grows out.
Summing up Permanent bonds; if you want to break bridges, as in those strong Disulphide Bonds, you can add a reducing agent. And if you want to build bridges, you add an oxidizing agent. Ones commonly used for hair perms and straighteners are ammonium thioglycolate as a reductant to break the bonds & hydrogen peroxide as the oxidant to reform them. But similarly, reducing and oxidising agents can be found in bleaches, which is where plexes/bond-builders are making an impact. Definitely a blog for another day.
Temporary bonds; remember the charm bracelet and the intertwining and interacting side chains or charms. There are still the remaining 19 amino acids that make up our hair accounting for well over 2/3 of the hair’s structure. Temporary bonds are weak bonds (non-covalent bonds) and can be easily reversible, it might be easier to think of them as attractions rather than bonds. The attraction comes from charges and/or partial charges liking each other. If the charges are full you can get an “ionic bond” (aka salt bridge). These are relatively strong, but still not as strong as covalent bonds.
Noncovalent bonds may be individually weak, but when you have a lot of them each contributing it can really add up. In the middle strength-wise you have hydrogen bonds that are easily attracted to oxygen… it has a lot to do with electron sharing, but suffice to say that when water is added or absorbed by hair H20 (with its own chemistry) the hydrogen bonds lose their attraction in favour of the water’s oxygen. Seemingly Oxygen is a little promiscuous when it comes to sharing its electrons. You’ve probably worked it out already, but this is why wet hair is more prone to damage than dry hair as our temporary bonds are being distracted elsewhere. Reinforcing the importance of our temporary bonds.
Both hydrogen and salt bonds are an integral part of the hair and help to give the Keratin its stretchiness or as we like to call it in the professional elasticity and bounce. They also allow us to temporarily curl, straighten and shape our hair and when we fancy washed it out and change it up again.
Summing up temporary bonds; they may be weak in chemistry terms but they are not weak when it comes to our hair’s structure. If you want to break temporary bonds you introduce another ‘attraction’ e.g., water H20, they will naturally return to their original paring once the attraction has been removed; drying the hair.
I would like to share an analogy I like to use when coaching on bonds, Think of our hair as a house. Our Permanent bonds are the brick and mortar of the building and our Temporary bonds are the doors, windows and roof. You need both to make the house strong, weather proof and liveable. Similarly, with our hair, all of the bonds have a role to play.
If you take away one thing from reading this today, it is that all our hair bonds are important in maintain the hair’s integrity.
Stay safe and well
Caroline
