The chemistry behind Hair Dye

The concept of being able to change hair colour is fascinating, and there are many different types of ways to do it.

Foremost, the molecules that cause our hair to be coloured in the first place are pigments called melanin or more specifically, eumelanin and pheomelanin. Eumelanin is the pigment in charge of brown and black shades and pheomelanin gives blonde to red shades. This means that darker hair contains more eumelanin (the more abundant type) and lighter hair colours contain primarily pheomelanin. Different shades of hair colour simply depends on the ratio of concentrations of the two pigments.

The hair is structured as concentric cylinders made up of three layers. The outer layer is the cuticle which is transparent and protects the cortex, made up of lots of overlapping dead cells. The middle layer is the cortex, which provides the strength, moisture, colour and texture to the hair (melanin is found in the cortex) and the inner layer is the medulla, which is the core of the hair and may be absent in some cases.

Now that we know a little about the chemistry of natural hair, we can talk more about dyeing them. As many will know, there are different ways to change the colour of your hair, ranging from temporary dye to permanent dye.

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Temporary hair dye is quite popular for those who want a short term change. It does not actually change the natural hair colour as the dye does not penetrate the cuticle at all, it merely attaches itself to it, meaning that they don’t damage the hair at all. This means that after a certain amount of time, the colour will be washed out as the hair is washed. However, these conditions also means that temporary hair dye is not effective on people with naturally dark hair as the dye on the cuticle does not show. Common examples of temporary hair dye are hair colour sprays and hair chalk; these both wash out in one wash meaning they are very short term.

Semi-permanent hair dyes are perfect for those who wish to have a longer lasting change and they’re also great for grey hair coverage. They penetrate the cuticle without reaching the cortex and covering the natural pigments (this could be a downside as it limits the colour palette meaning those with darker hair may find it difficult to work with this type of dye). They do not damage the hair structure at all which is a bonus but the colour fades and disappears after usually four to six weeks.

The chemistry behind permanent dyes is a little more complicated as there are a number of new chemicals involved in permanent dyes, of which some are what harms the hair. First of all, the natural pigments in the cortex must be removed and replaced with dyes for the colour to stay permanently, which is why this is the most effective way for those with dark hair to change their hair colour. In order to do this, the cuticle is opened and lifted by using an alkaline chemical with a pH of around 10, usually ammonia. Next, in order for the dye to show more prominently, hydrogen peroxide (commonly known as bleach) is used to lighten the hair. This is done by oxidising melanin, essentially reacting with the melanin and turning them into colourless chemicals. Now, small precursor molecules (the dye) are soaked into the cortex through the open cuticle and they react with one another, forming larger molecules too big to escape the cuticle layer. Consequently, the cuticle is closed by an acidic conditioner but it is more damaged and fragile in comparison to the start.

Although permanent hair dyes do not need to be reapplied, they can not be washed out if you decide the colour isn’t that great anymore, unless the hair is bleached again and recoloured or you could wait until new hair grows out. Continuous bleaching distorts the cuticle layer repeatedly, damaging the hair more and more due to the toxic chemicals used, which is why it is advised not to excessively bleach your hair.

By Lulu Aberg

The Chemistry Behind How Alcohol Affects the Body

Many of us may be familiar with the typical symptoms after alcohol consumption such as feeling a change in mood, being more relaxed and change in behaviour. But have you ever considered what might be going on in the body to make these effects?

First let’s look at how alcohol is made. The alcohol that is used in drinks for consumption purposes is ethanol, which is produced through a process of fermentation. To begin, sugar or starch is dissolved in water and yeast is added. This mixture is then fermented anaerobically (without presence of oxygen) at a temperature between 30-35°C. The environment in the last step forces the yeast to respire anaerobically which uses up the glucose (in the sugar), and produces ethanol and carbon dioxide [1](as shown in Fig1).

As seen in the formula of ethanol in the photo, ethanol has an -OH (hydroxy) group which allows ethanol to have the ability of hydrogen bonding. Hydrogen bonding is an intermolecular force found between molecules. This is why ethanol is soluble in water, as water molecules are also able to make hydrogen bonds allowing for hydrogen bonds to form between ethanol molecules and water molecules(Fig2). Ethanol’s solubility means that it can easily be absorbed into the bloodstream and can travel around the body very quickly. Alcohol is distributed through the body via the bloodstream, so most tissues are exposed to the same concentration of alcohol as in the blood. An exception of this is the liver which digests about 90% of alcohol before it passes through into the rest of the body.

Very little alcohol diffuses into the fat as fat has a very low solubility due to it having little water. Alcohol diffuses fastest into the organs such as the heart, brain, and lungs which have a high blood supply that maintains a steep

concentration gradient for maximum rate of diffusion.

The behavioural effects of alcohol can be explained by how alcohol affects the neurotransmitters (‘messengers’) in the brain. When you consume alcohol, the amount of GABA (a neurotransmitter that dampens your responses) increases. As a result there's a reduction in communication in your brain cells you experience a decrease in your judgement and decision making, motor and visual responses are also slowed down.

The liver uses an enzyme called alcohol dehydrogenase to convert alcohol into a toxic substance called acetaldehyde which is easier to break down and helps with removing alcohol from your system. Acetaldehyde is then broken down by the enzyme aldehyde dehydrogenase into acetate. Acetate is then further metabolised and eventually leaves the body as water and carbon dioxide. This often does not occur at the site of the liver, and rather is

metabolised in the heart, skeletal muscle and brain cells.

Consuming food, especially carbohydrates, before drinking alcohol strongly affects how much the alcohol will physically affect you. By eating food, this lines the stomach and prevents the alcohol from rushing straight into the bloodstream. This then means the alcohol is released more slowly from the intestine, which gives the liver more time to break down the alcohol resulting in less alcohol circulating the blood stream and a weekend effect. However, drinking fizzy alcohol increases the pressure in your stomach which forces alcohol into your bloodstream faster.

By Grace Kaprielian

Sources used: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC54 3875/

https://www.bbc.com/news/newsbeat-30350860