The Science of Hair Colour
Hair colour results from melanin variations, structural characteristics, and can be altered temporarily or permanently through chemical processes.
This article delves into the fascinating science behind hair colour, exploring its natural origins and the various methods used to alter it.
The Natural Palette: Melanin and Hair Structure
The natural colour of human hair is primarily determined by two types of melanin, a pigment produced by specialized cells called melanocytes within the hair follicles.
- Eumelanin: This pigment is responsible for black and brown hair colours. Higher concentrations of eumelanin result in darker hair.
- Pheomelanin: This pigment contributes to red and yellow tones. The presence of pheomelanin, often in combination with lower eumelanin levels, leads to red, ginger, and blonde hair.
The specific ratio and amount of these two melanins produce the wide spectrum of natural hair colours. Hair colour also varies due to genetic factors and ethnicity.
Beyond melanin, the structural characteristics of the hair strand itself play a role. The way light reflects off the hair's cuticle, the outermost layer of the hair shaft, can influence the perceived colour. For instance, tightly packed cuticles reflect light more evenly, contributing to a shinier appearance, which can subtly alter how a colour is perceived.
The Greying Process
As we age, the production of melanin by melanocytes gradually decreases. This reduction in pigment leads to the hair losing its natural colour and appearing grey, white, or silver. This process is often genetically determined, but external factors such as stress and diet can also influence its onset.
Altering Hair Colour: The Chemistry of Change
Commercial hair colour products utilize various chemical processes to either deposit new colour onto the hair or remove existing colour.
Temporary Colour
Temporary hair colours are typically large pigment molecules that coat the outside of the hair shaft, rather than penetrating it. They are designed to wash out with one or a few shampoos. This method is gentle on the hair as it does not require opening the cuticle or altering the internal structure of the hair.
Semi-Permanent and Demi-Permanent Colour
Semi-permanent colours contain smaller pigment molecules that can partially penetrate the hair cuticle. They don't use ammonia or peroxide to open the cuticle, making them less damaging than permanent colours. These colours typically last for 6-12 shampoos and gradually fade.
Demi-permanent colours use a low volume hydrogen peroxide developer, which opens the cuticle slightly, allowing the colour molecules to penetrate further into the hair shaft. They do not contain ammonia, which preserves the hair's natural melanin. Demi-permanent colours provide more vibrant results and better grey blending than semi-permanent options, typically lasting 12-24 shampoos.
Permanent Colour
Permanent hair colour involves a chemical reaction that opens the hair's cuticle and deposits new pigment into the cortex, the innermost layer of the hair shaft. This process typically uses two main components:
- Alkalizing Agent (Ammonia or derivatives): This agent swells the hair shaft and raises the cuticle, allowing the colour molecules to enter.
- Oxidative Dye Precursors and Developer (Hydrogen Peroxide): The dye precursors, small colourless molecules, penetrate the cortex. The hydrogen peroxide then oxidizes these precursors, causing them to expand and react with each other to form larger, coloured molecules that are trapped within the hair. This new colour is permanent because the molecules are too large to be washed out.
Permanent colours can lighten hair by breaking down natural melanin and deposit new colour. They offer the most significant colour change and long-lasting results but can also be the most damaging due to the chemical processes involved. The pH of permanent hair colour formulations is typically alkaline, ranging from 9 to 11, to facilitate cuticle opening.
Bleaching and Lightening
Bleaching is a process that removes natural or artificial pigment from the hair, resulting in a lighter colour. It involves the use of an alkaline agent (like ammonia) and an oxidizing agent (hydrogen peroxide), which penetrate the hair shaft and break down the melanin granules. This process is irreversible and can significantly weaken the hair structure if not performed carefully.
The Role of pH
pH (potential of hydrogen) is a crucial factor in hair colouring. The natural pH of hair and scalp is slightly acidic, typically between 4.5 and 5.5. Most hair colouring processes, especially permanent ones, involve alkaline solutions to lift the cuticle and allow pigment penetration. After colouring, it is important to use acidic products to help reseal the cuticle and restore the hair's natural pH, thus minimizing damage and prolonging colour.
Colour Theory in Hairdressing
Understanding colour theory is essential for achieving desired hair colour results. The basic principles include:
- Primary Colours (Red, Yellow, Blue): These cannot be created by mixing other colours.
- Secondary Colours (Orange, Green, Violet): Created by mixing two primary colours.
- Tertiary Colours: Created by mixing a primary and a secondary colour.
- Complementary Colours: Colours opposite each other on the colour wheel (e.g., yellow and violet) that neutralize each other when mixed. This principle is used to counteract unwanted tones, such as using violet-toned products to reduce brassiness in blonde hair.
Hair Colour Care
Maintaining coloured hair involves specific care to preserve vibrancy and health. This includes using colour-safe shampoos and conditioners, avoiding excessive heat styling, and protecting hair from UV exposure. Products designed for colour-treated hair often contain ingredients that help to seal the cuticle and prevent colour fade.
Find these ingredients in Watermans products
- Ginger — you will find this ingredient in our Menopause Relief Kit.