Ingredients like palm oil are criticised, often correctly, for their impact on our climate. But what else in our shampoos and soaps could be increasing our shower emissions?

The back of the shampoo bottle I use has a long list of ingredients and a few claims about their origins. It boasts of things like “containing 0% silicones” and natural ingredients, and while I have a reasonable grasp of what goes into soaps and cosmetics, I have often wondered what some of these ingredients do – and whether they are good or bad for the climate.

The bottle says my shampoo is made from 95% natural-origin ingredients – this breaks down into 73% water, 22% other naturally derived ingredients, with the final 5% made up of synthetic ingredients.

The main ingredient in liquid soaps, shampoos and conditioners is perhaps unsurprisingly water (or “aqua” on most bottles). But after water, one of the next most voluminous ingredients in my shampoo is sodium laureth sulfate (SLES), which can be made from palm or coconut oil. SLES is used as a surfactant – a chemical that helps to emulsify oils and water. It has several roles in shampoos, as well as toothpastes, soaps and face washes. Firstly it is a detergent, which is a type of chemical which makes proteins and fats soluble in water, making them easier to wash away. It also acts as a foaming agent, without which shampoo would be disappointingly un-bubbly.

Next on the ingredients of my shampoo are various chemicals that are a mouthful to pronounce, from cocamidopropyl betaine (a coconut oil derivative) to guar hydroxypropyltrimonium chloride (a gum derivative that helps to make hair easier to comb). Some of these chemicals are stabilisers, preservatives, colourants and fragrances that keep the product looking and smelling the same with every use.

I want to know where these ingredients come from. Are any of them damaging to the climate to produce? And if I produced my own soaps and shampoos, would it be better for the planet?

To answer that question, I need to know the emissions produced by commercial shampoos.

The environmental impact of washing your hair is highly dependent on your showering (or bathing) habits. The amount of water you use, and the temperature you set the thermostat to, will have a significant impact on the emissions from your shower. Add to this the regional differences in how water is heated, and the source of that power, and coming to a single universal figure for the emissions from one wash is practically impossible.

In one study based on people showering in Switzerland, one hair wash using one brand of a plant-based shampoo generated greenhouse gas emissions equivalent to 161g CO2 (CO2e) – which is about the same as driving a petrol-powered car half a mile. But Zurich, the city in which the study was conducted, relies on predominantly fossil fuel-based heating, note the authors Hanna Kröhnert and Matthias Stucki from the Zurich University of Applied Sciences. In other cities and countries with lower-carbon sources of heat, the figure might be lower.

There are a few assumptions in these calculations, including that we use 15 litres of water when we wash our hair, and like our showers to be 38C (100F). If you spend a little longer, or prefer your shower warmer, your emissions will be higher.

Manufacturing shampoo, including all aspects from heating the offices of the cosmetic companies to the electricity used in the factories, contributed more in CO2e (19% of the total) than the emissions from the production of the ingredients (5%), the manufacturing of the packaging (4%) and distribution to the retailers (8%).

But comfortably the biggest contributor to the CO2e emissions from your hair wash is the energy used to heat your shower – 62% of all the emissions come from the water.

What about other impacts on the environment? Kröhnert and Stucki also looked at eutrophication (the leaching of nitrogen and phosphorus into waterways, causing blooms of algae which kills off other aquatic life) and ecotoxicity (where toxins are released that directly kill wildlife).

The single ingredient that caused the highest amount of eutrophication and ecotoxicity in their shampoo is propanediol, which is used in a lot of cosmetics to give them a runny but viscous texture. Propanediol can be manufactured from petrochemicals or, in this case, from corn. Stucki notes the reason propanediol score quite highly for impact on eutrophication and ecotoxicity is because it makes up a large volume of the ingredients of the shampoo. Corn production uses pesticides, which can leach into the environment. Again, though, the eutrophication and ecotoxicity caused by heating water is greater.

Another environmental consideration from cosmetics is land use. Kröhnert and Stucki point out that plant-based shampoos, like the one they studied and the one in my bathroom, are likely to use more land than petrochemical-based shampoos.

After we have rinsed the shampoo from our hair, what happens to those chemicals next? Some bathroom cosmetics, like face scrubs, exfoliators and soaps, contain microbeads – which are usually made from plastics such as nylon or polyethylene. These beads are used to create an abrasive texture to help clean our skin, but they are not only reserved for scrubs – they are also present in shampoos, deodorants and lipstick.

After washing down our drains, microplastics leach into our waterways and seas, where they have been found in fish. Because plastic takes so long to degrade, the concern is that once in the food chain it will remain there for a long time, being passed up the chain from species to species. In a recent study from 2022, microplastics were found in blood samples from members of the public for the first time. Their presence is toxic to human cells.

But some of these climate costs could be avoidable. There is a growing fashion for solid shampoos, which do not contain ingredients like propanediol (because they don’t need to be viscous) or large amounts of water. Reducing the water weight in the product would reduce emissions from transportation, says Stucki. Solid shampoos are also sold as having less packaging, but Stucki is most interested in how they change showering behaviour.

"It would be interesting to know if using a solid shampoo leads people to take longer or shorter showers with more or less hot water," he says. "Solid shampoo would have the biggest environmental savings, if it would prompt people to use less hot water and less shampoo. That would be an interesting experiment to conduct."

Solid shampoos are in essence bars of soap. Could I make my own? I have a little bit of experience making soap. For a few summers while a student I would help my sister with her handmade soap company, so I know that the fundamental ingredients of soap are water, fat and lye – which is another word for sodium hydroxide (sometimes also called caustic soda).

The lye helps to solidify soap into a hard bar by breaking down the fat into fatty acid chains (liquid soaps and shampoos often also contain sodium hydroxide for its detergent properties).

Historically, soaps would have been made with rendered animal fats and lye made from ashes mixed with water. Thankfully, we have moved on a bit from then and the soaps I made used coconut and palm oil, and sodium hydroxide powder mixed with water. The process is quite therapeutic – watching over pans of melting coconut oil, the scent of essential oils wafting around.

There are two methods of producing soaps: the "hot" and "cold" processes. They are very similar, except in the hot process the mixture is heated on a hob, which is the one I used. When you drop the lye into the warm oil it starts an endothermic reaction. The pan suddenly goes from warm to very cold as heat is absorbed from the surrounds into the mixture to power the chemical reaction.

The extra energy used in the hot method speeds up the setting and curing time, but if you were very keen to reduce emissions, you could be patient and opt for the cold method.

The mixture is then left to set and cure to allow water and any residue sodium hydroxide to evaporate away. Because of the sodium hydroxide, initially the mixture might be very irritating to the touch, so handmade soaps might need to be left for several weeks before they are fully cured and ready to use.

If you are prepared to wait this long for your bar of soap, it can be a money-saver. Even in small batches, homemade soaps, shampoos and shower gels can be significantly cheaper than consumer products. The soaps I made (in batches of 24) cost between 30-40p (40-50 cents) each.

There are some unavoidable environmental costs from homemade soap. Some plant-based soaps use coconut and palm oil, which depending on how they are produced can have significant negatives. More than 90% of global palm oil is produced in Borneo, Sumatra and the Malay Peninsula, but oil palm plantations in this region are expanding into tropical forests, leading to 50% deforestation in Malaysian Borneo, for example. Oil palm also contributes to peatland draining and burning in Southeast Asia. Peatlands are enormously important for storing carbon. Despite only covering 3% of the world’s surface, they sequester twice the amount of carbon as the world’s forests.

Alternatively, you can use other plant-based oils like olive oil and castor oil. Though palm oil can be a good choice if it is sustainably sourced, as it is a more productive crop than other oils.

If you would like your homemade solid shampoo to have a fragrance, then you will also need to include essential oils. While they only account for a very small fraction of the ingredients (sometimes less than 1% by mass), according to Kröhnert and Stucki’s research they are one of the larger contributors to environmental costs like land use and eutrophication.

So, if you are keen to reduce the emissions from your shower, perhaps it is worth making your own simple, solid shampoo. But an even easier solution? Turn down the temperature of the water a degree or two.

BBC

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