Permanent Waves: How does the molecular structure of your hair change to create a permanent shape?

Permanent waves are an easy, sustainable hairstyling option for busy people that works by changing the molecular structure of your hair so that it stays the way you want it for longer. Based on the scientific principle of changing hair through oxidation and reduction reactions, this procedure is more permanent than temporary methods like blow-drying.

 

How much time do you need to touch your hair on a busy morning as you get ready for work? While the exact amount of time varies from person to person, getting a permanent wave, commonly referred to as a “perm,” is a quicker and easier way to style your hair than blow-drying or waxing it every day. Permanent means “permanent,” which means that once you have it done, it will keep its shape even when you wash your hair. Also, unlike temporary styling tools, permanent waves allow you to keep your hairstyle for a longer period of time, making them a great option for busy people. Unlike blow-drying, which uses heat to remove moisture from the hair to temporarily hold its shape, perming alters the molecular structure of the hair through oxidation and reduction. This structural change is more than just styling, it’s a fundamental transformation.
Without special chemicals, your hair will quickly return to its original shape, even if you bend or twist it arbitrarily. This is because cystine, the protein that makes up hair, is linked by sulfur-sulfur bonds to cystine in other hair proteins, forming a ladder-like structure where neighboring protein molecules are linked by sulfur-sulfur bonds. This structure is an important factor in determining the elasticity of hair, helping it to maintain its natural shape. Because the sulfur-sulfur bonds that connect neighboring proteins are covalent, they are stronger than other intermolecular bonds that are temporarily formed depending on the shape of the hair. Therefore, sulfur-sulfur bonds can be responsible for returning bent hair to its original shape, and breaking the sulfur-sulfur bonds (S-S) of the cystine ladder is important for reshaping hair into a different shape.

 

 

So how do we break the sulfur-sulfur bonds of the cystine ladder? The sulfur-sulfur bond is a covalent bond, meaning that each atom gives one electron to the other, for a total of two electrons shared between the two atoms. Each sulfur atom gets both electrons shared through this bond, so it’s like having an extra electron. However, there is a limitation: because the bond is between identical sulfur, the electrons are not close enough together. In other words, if you think of the atoms in this bond as magnets and the electrons as iron powder, the magnets on either side of the bond have the same force, so the iron powder will be in the exact center of the two magnets, and the iron powder will be farther away from the magnets than if there were no opposing magnets. The nature of this bond is one of the reasons why it is difficult for hair to maintain a specific shape.
So, to break the sulfur-sulfur bond, the sulfur atom needs to bond with an atom that has a weaker ability to attract electrons, so that it can more easily attract electrons without having the effect of having one more electron than it already has. If there is such an atom nearby, the sulfur atom will break the sulfur-sulfur covalent bond that attracts electrons with equal force and form a new covalent bond with an atom that is weaker at attracting electrons. In this case, the effect of the sulfur atom having an extra electron is maintained because the two equally bonded atoms share two electrons by giving one away, but the electron is located closer to the sulfur atom because the sulfur atom has a stronger attraction to the electron. The key to this process is to ensure that the hair is able to stabilize its modified shape through new bonds. The most common bond is hydrogen (H), and this bonding of any atom to hydrogen is called “reduction”. So, when the reducing agent is applied in the first step of the process, each sulfur bonds with a hydrogen atom and the sulfur-sulfur bond is broken, allowing the hair to reshape.
However, just because the hair is able to change shape by breaking the bonds that hold it in place doesn’t mean that it will stay in the desired shape. The reshaped hair is still in an unstable state, and if left alone, the hair will tend to revert back to its original shape. Once the sulfur-sulfur bonds in the hair have been broken with a reducing agent, and the hair has been rolled into a cylindrical appliance in the desired shape, the hair needs to be locked into that shape. During this process, the sulfur loses a hydrogen atom, and this process of taking a hydrogen atom away from an atom is called “oxidation”. The oxidizing agent, the component that causes this reaction, is made up of atoms that attract electrons more strongly than sulfur atoms. Therefore, the oxidizing agent tends to bond with hydrogen, which has a weaker attraction to electrons, to make it more comfortable for the electron, so the sulfur atom, which is weaker than the oxidizing agent, loses its hydrogen and forms a sulfur-sulfur bond with the neighboring sulfur atom. Heat accelerates the rate at which new sulfur-sulfur bonds are formed, which is why heat pumps, a type of perm, are often applied with an oxidizer followed by heat. This process creates new sulfur-sulfur bonds, and these bonds are the force that holds the hair in shape, which is why the rounded shape of the hair is maintained.
In this way, perming is a procedure that uses oxidation and reduction reactions to change the molecular structure of the hair, which in turn changes the shape of the hair. It’s not just a cosmetic procedure, it’s based on scientific principles, and the results can last for a long time. It’s a very stable and permanent method because it creates new bonds, but it’s not guaranteed to last forever because gravity is constantly acting on the hair and chemicals, such as shampoos and conditioners, are regularly applied to it. Also, changes in the external environment and hair growth can affect the maintenance of a perm over time. However, considering that temporary hair styling using conventional heat, such as blow-drying, is released by water, permanent waves, which change the shape of the hair at the molecular level, can be considered a literally ‘permanent’ hair styling method.