Growing up, my mom always bought bars of soap. When I became a teenager, I got in the habit of asking my mom for liquid soap. Why? Because they smell good, come in pretty packaging, are easier to use in the shower, and also store better in the shower (in my opinion at the time). I hated struggling with a slippery bar of soap, have it sit in water, and break apart. I kept those habits when I moved out and started buying my own showering products. When I lived with roommates, I became worried others were using my bar of soap and the idea of sharing that disgusted me. But now, as I become more curious about the implications my decisions have on the environment, I question whether I should be buying liquid soap at all. So I scoured the internet for all the info I could find about which is better.
What is soap?
First and foremost, what is soap? Soap is a product made of fats/oils and an alkali (usually lye). I knew this, having spent many hours on youtube watching soap makers share how they make their products (I highly recommend it by the way. A great way to relieve stress). Based on this definition of what soap is, many people are not washing themselves with soap and are, in actuality, washing themselves with “detergent”. Body wash is made with chemicals called surfactants. Even some bars of soap are not actually soap (4). This surprised me, as I had never really considered the difference.
Although liquid soap is a common household item today, it wasn;t always the case. It was patented in 1865 by William Shepphard but was used mostly for industrial purposes. It wasn;t until the 1980s that liquid soap started to make it’s way into people’s homes. To convince people to buy it, it needed to have a benefit. As companies began to invest on the household priority of CONVENIENCE, the pump dispenser entered the market. The pump makes liquid soap easier to use than a traditional bar of soap, but at what cost (environmentally, economically, and well as health related). That is what I wanted to find out.
Finding the categories
I started by reading “Comparing the Environmental Footprints of Home-Care and Personal-Hygiene Products: The Relevance of Different Life-Cycle Phases”, a study done in 2009 (Availability for you to read here). Although it was very technical and had a lot of long words I was not familiar with, I found it a good starting point for understand what points to compare. Here is their initial diagram describing the life cycle of products and where it can have environmental implications.
Figure 1
The LCA model and its system boundaries
With this image, I got a good idea of the life cycle of a product and I came up with several areas to compare including: production, transportation, energy requirement, packaging, waste production/disposal, and wastewater treatment. I also wanted to look at water use, ingredients/quality, as well as cost (to the consumer). Table 1 shows a summary of the results.
Table 1
Sustainability of Liquid soap versus bar soap
 |  | |
| Carbon Footprint | Liquid soap has a carbon footprint about 25% bigger or 10x more than a bar of soap (1,5). |  |
| Production (energy) | Liquid soap requires 5x more energy to produce (1). | |
| Packaging (Waste) | Liquid soap often comes in plastic containers or large plastic bags. Although these can sometimes be recycled, whether they are actually recycled is another question and doesn’t beat the biodegradable/ cardboard packaging possible with bars of soap (7). | |
| Packaging (energy) | Liquid soap requires 20x more energy to package (1) | |
| Transport | Liquid soap is generally heavier and therefore uses more fossil fuels to transport (2,7). Even if we went all electric, it would require more of the car’s battery to transport if the load was heavier. Not only are bars of soap lighter, their shape (usually a rectangular prism) make them easier to stack and transport, compared to the rounded shape of bottles (5). Their shape also makes them easier to store for sellers, meaning they don’t require shipments as large or as often (5). | |
| Amount used | We use more liquid soap compared to a bar of soap when we wash our hands (1). In a 30 second hand-wash, people on average use 0.35g of bar soap compared to 2.3g of liquid soap. Therefore, liquid soap uses more than 6 times more than bar soap (5). | |
| Ingredients (health) | Liquid soap is made with petroleum based surfactants that come with environmental impacts (1). Liquid soap is often also made with SLS (sodium dodecyl sulfate), sulfates, and dyes. These all have potential negative impacts on the environment as well as your own skin (3). Bar soaps are generally made with more natural ingredients compared to liquid soap (6), but this can definitely vary depending on the brand. | |
| Land use | | Ingredients used for bars of soap, namely vegetable oils, usually come from farmed crops and tend to take up quite a bit of land (5). Some bars of soap are made from oils that have a dire environmental impact on forests when produced on a large scale, such as palm oil (1). |
| Water used (hand washing/ bathing) | | It takes a bit more time to wash our hands with a bar of soap and therefore uses more water (about 30% more heated water) (1) |
| Water used (production) | It takes about 30% more water to produce liquid soap than bar soap (2,3,6). | |
| Wastewater treatment | Liquid soap requires more wastewater treatment (5). | |
| Cost | Usually, a bar of soap is more cost-effective than liquid soap. If you start to insist on buying locally and buying very good products, it may cost more than the average bottle of liquid soap (7). However, we must consider that the good quality bar of soap will probably last longer, so you are not paying much more for it in the end. A liquid soap of equal quality may cost just as much if not more. | |
Verdict?
Although your choice of soap may not have as much of an impact on the environment as, say, modes of transport or diet, we need to assume that everything we do matters and we should try, whenever we can, to decrease our environmental impact. That said, bars of soap use less water, less energy to produce and transport, and less packaging, meaning less waste. Although not environmentally relevant, bar soap is also usually better for our skin than liquid soap. So there you have it, bar soap is better than liquid soap in almost every aspect.
What more can you do?
Think about the packaging
Look for soaps that come with minimal to no packaging. Avoid soaps that have plastic overwraps or have several layers of packaging. Try to find soap makers that package their soaps in biodegradable or recyclable cardboard boxes. And furthermore, do the best you can to properly dispose of that packaging by putting it in the right waste basket (garbage/recycling/compost).
Think about what your soap is made out of
You can find more info about that here. Other ingredients to avoid include: triclosan, parabens (methylparaben, propylparaben, and butylparaben),sulfates (SLS [sodium lauryl sulfate] and SLES [sodium laureth sulfate]), and fragrances. These can be bad not only for the environment, but also for your skin. You can go here to search toxicity levels of different products and ingredients. Avoid soaps that are made with palm oil or make sure it is made with sustainable palm oil.
Think about where your soap came from
The best way to decrease your carbon footprint surrounding soap is to buy locally. Although sometimes this can come with a bigger price tag, supporting local business and small business owners is not only good for the economy where you live but also minimizes transport related carbon emissions.
Try to make your bar of soap last as long as possible
There are certain things you can do to make your bar of soap last even longer. This includes unwrapping a bar of soap to let it dry out for several weeks before using it. When the soap is dry, it doesn’t dissolve as fast when it comes into contact with water.
Another obvious way to make your bar of soap last longer is to minimize its exposure to water. The first trick is to cut the bar of soap into two (or more) pieces to avoid the entire bar of soap being exposed to water. Another important trick is to keep the bar dry between washes. You can do this by making sure you have appropriate drainage or making sure there is no water in the soap dish. I haven’t tried either of these but I would really love to.
Finally, don’t throw away the last bit of soap left at the end of the bar of soap. You can dissolve it in water and use the water to wash or you can even stick it to the new bar of soap.
Conserve water
Since the major downfall of the bar of soap was water usage due to taking longer to wash your hands, try to remember to turn off the water while you are washing your hands and only turn on the tap to wet and rinse. This is something I was always very lazy about but have recently introduced into my hand washing routine.
Make your own soap
If you have a very adventurous side, you can even try making your own soap. Although soap making can get quite expensive, since you’ll need a lot of products that are often sold in bulk and will also need the proper material to successfully make a soap. Making your own soap can be very satisfying, knowing all the ingredients in what you’re putting on your body. You could also make up for costs by selling some high quality bars of soap to friends and family.
What can you do if you want to continue using liquid soap? (and that’s totally OK)
Since the main disadvantage of liquid soap is the packaging, you can decrease your environmental impact by going around the packaging (5).
- Try buying in bulk and refilling dispensers. This uses less plastic and can even be cost-effective.
- To avoid packaging altogether, find stores in your area where you can purchase liquid soap without a container at all. You can bring your own bottle and pay per weight. Although these stores may be hard to find, it would be the best way to avoid consuming and using the very wasteful packaging of liquid soap.
References
(1) https://theecoguide.org/liquid-vs-bar-soap-which-more-environmentally-friendly
(2) https://www.weekand.com/home-garden/article/green-bar-soap-instead-body-washes-18053450.php
(3) https://www.greenmatters.com/p/soap-bad-for-environment
(4) https://pubs.acs.org/doi/abs/10.1021/es901236f
(5) https://www.zmescience.com/feature-post/pieces/feature-solid-soap-liquid-soap-environment-29052020/
(8) https://www.goodhousekeeping.com/beauty/anti-aging/tips/a18342/recycle-soap/