Hi! Welcome back to our serial Hair Dyeing: Cool! And… Last time we talked about hair and its composition. This time, let’t talk about how different types of hair dyes work.

What determines hair color?

Recall from part 1, our hair consists of cuticle (outer layer), cortex (middle) and medulla (inner). In addition to keratin that locates in the cortex, another type of protein, melanin, exists in cortex as well. Melanin gives the hair its color, and below are the two main types of melanin:

• Eumelanins: give hair dark colors
• Pheomelanins: give hair light colors

How do I do hair dyeing: Different types of hair dyes

There are three main types of hair dyes, and they are

• Temporary hair dyes
• Semi-permanent hair dyes
• Permanent hair dyes.

Temporary hair dyes do not last long, and can normally be washed off using one shampoo. Chemically, it is “nonoxidative”, which is a physical change. The composition, according to National Library of Medicine, is water-soluble acidic and basic dyes bearing azo or anthraquinone groups. Temporary hair dyes are “paint-like“, which is deposited on the cuticle of the hair (or it coats the hair). Molecules sit on top of the hair, and do not get into the cortex of the hair.

Semi-permanent hair dyes are similar to temporary hair dyes, but the molecules are rather smaller, or the molecular weight is smaller, the molecules also go deeper in to the cuticle, the surface of the hair. This type of hair dye, however, takes 5-8 shampoos.

What is key in temporary/semi-permanent hair dyeing?

A key concept here is porosity, thanks to Strands of Inspiration. Whether how stick is the hair dye is to the hair depends on the porosity of hair, as porosity means the ability of hair to absorb and retain moisture, according to Clever Curl. As a result, corresponding to the image below, if the hair is more porous (right), the particles and settle more tightly and deeply in the cuticle, and if the opposite (left), they would be washed away very easily.

What about permanent and demi-permanent (another type of hair dyes, between permanent and semi-permanent)?

The previous section is about physical changes, and these two types of hair dyes are more of chemical changes (as they are known as oxidative). This usually happens in the cortex, and the chemical structure in your hair is usually altered. When doing permanent or demi-permanent hair dyeing, chemicals such as ammonia and hydrogen peroxide are used.

Ammonia: Ammonia is used to open up your cuticle, and it can then let the other chemicals to enter your hair. This is due to their high pH of 10-11.

Hydrogen peroxide (the developer): What does H2O2 do? First, it breaks the carbon-carbon double bonds, thus the melanin is broken. This results in the loss of your natural hair color, and your hair becomes colorless. Second, H2O2 also serves to react with hair dye chemicals in order to produce colors. To be specific, it kick-starts the oxidative hair dye process, along with two hair dye chemicals (primary and secondary). H2O2 thus reacts with these two dyes and produce beautiful colors, according to Ms Beautyphile.

Demi-permanent differs from permanent hair dyeing as the former does not really contain ammonia, which does not permanently alter the hair like the latter does, according to Miranda Mondry. It can take up to 24 washes.

Above is something about hair dyeing chemistry. Hair dyeing is cool, as how much chemistry it has applied, and how diverse it can be. Next type we will explore how hair dyeing associates with our health. Please comment and share any hair dyeing experience you have had!