What are salt bonds and how do they work?

Firstly, let’s look at the Cortex, the inner most part of the hair structure, to really understand what these “Ionic” bonds do.

The cortex is the main bulk (as much as 90% of the total mass) of a hair strand. This part of the hair determines:

1. Strength
2. Flexibility
3. Elasticity
4. Texture 
5. Colour 

Let’s concentrate on the strength, elasticity and flexibility of the hair structure:

The cortex is made up of long protein chains attached by “peptide” bonds at each end (you may know of these as polypeptide chains). 

These long chains are made up of “amino acids” (the smallest part of a protein, keratin is made up of around 19 different amino acids) and are closely linked together. 

These long chains coil around each other to make a firm structure. There are millions of these chains that make up the cortex in one strand of hair.

This structure is closely linked together by side bonds. 

Salt bonds are found within this compacted structure and work to keep the cortex together by linking one amino to another side by side. This action keeps the hair strand tightly compacted, strong and in a healthy state.

There are 3 types of side bonds- Salt, Hydrogen and Sulphur. 

Salt bonds are a “physical” bond (meaning the characteristics of this property can be changed without a chemical reaction) and work ionically. 

The salt bond occurs when the negative “charge” of one amino acid is attracted to the positive charge of another (think about magnets when they attract).

Salt bonds need an acidic pH level (around a 4.5-5.5) for this ionic attraction to be able to occur. 

When the pH of the hair is changed the more these links will be broken, this physical change can be made by heat, water, friction and tension.

Two out of these three side bonds work ionically, Salt and Hydrogen, the more the hair is taken into an alkaline state the less attraction occurs, as the hair swells.

Salt bonds have a stronger attraction than hydrogen bonds, there are so many of them that they contribute to around 1/3 of the cortex total strength. They aren’t as affected by water (like hydrogen bonds) but are physically affected by heat and strong alkaline or acidic solutions. 

The great thing about these side bonds is when the hair is taken back into a comfortable pH level the attraction may occur again.

However even though the hair will want to repair itself, sometimes the damage is too much and that attraction will no longer be there.

So next time you use your heating tool think about the salt bonds and the connection.

Find out more about hair science via the Chaulk website ❣️

Big Love 

Sarah