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17 Feb 2020 : Shower Gel or Soap: which is better financially and environmentally? #
Today I want to tackle one of the really big questions of our time: which is better, soap or shower gel?

For a long time I thought shower gel was basically just watered-down soap and therefore couldn't possibly be better value. I can add water to soap myself, thank you very much. But shower gel and soap are actually made in quite different ways. They're both produced through a process called saponification (yes, honestly; probably coined by the same person who came up with Unobtanium), whereby fat or oil reacts with an alkali. However, while the alkali used in the production of soap is sodium hydroxide, for liquid soaps potassium hydroxide is used instead.

Still, what you end up with in both cases is an emulsifier that makes it easier to remove oil related stuff from your skin. There are two questions which really interest me. First, which is the cheaper in use, and second which is the more environmentally friendly.

To answer the first, I performed a couple of experiments. I bought some basic soap and shower gel products from Lidl's Cien range (that's Cien, not Chien). I think it's fair to say they're both value products, which makes them great for comparison.
 
Shower gel (left) and soap (right)

Here are their vital stats (as of June 2019).
  1. Lidl Cien Shower Gel: 300 ml (309g actual contents weight) costing €0.89.
  2. Lidl Cien Soap: 2 bars, 150g each (140g actual contents weight) costing €0.87.
So, that's a pretty similar cost-to-weight ratio. The question then is which of the two will last longer in practice. That 300g bottle of shower gel lasted me 19.5 days, whereas a single bar of soap lasted 26 days. So that gives a pretty convincing answer from the results.
 
  Cost per kg Usage per day Cost per day
Shower gel €2.89 15.85g €0.046
Soap €3.11 5.38g €0.017

These results are pretty clear-cut. I got through nearly three times as much shower gel per day compared to soap, making soap considerably less than half the cost of shower gel. So if your main concern is cost, soap is clearly the better option. Shower gel pretty much is watered-down soap after all.

But what about the environmental costs? There are many things to consider which make this a complex question and very challenging to answer. The transportation costs of soap will be less, because the daily weight used is less. However, in terms of the chemicals and energy needed for production, it's really hard to say.

The ingredients on the side of each packet aren't really very helpful, because the relative quantities are missing. Establishing the exact amounts turns out to be hard. However, I was able to get some relatively generic formulas from Ernest W. Flick's Cosmetic And Toiletry Formulations Volume 2. The formula for shower soap is given as follows.
 
Ingredient Quantity
Water and Preservative 29.3%
MONATERI 951A 20.8%
MONAMATE LNT-40 25.0%
Sipon LSB 17.9%
MONAMID 1089 5.0%
Ethylene Glycol Monostearate 2.0%

And here's the formula for shower gel.
 
Ingredient Quantity
Water q.s. to 100%
Standapol T 30%
Standapol E-1 10%
Lamepon S 9%
Standamid LDO 2.5%
Standamox LAO-30 3%
Sodium Chloride 2%
Kathon CG 0.05%

The "q.s." here is an abbreviation of "quantum satis", meaning "the amount which is enough".

Frankly, the only ingredient that means anything to me is "Water". But at least that's something. Based on this, we can roughly conclude that soap is approximately 29% water, 71% other, whereas shower gel is approximately 43% water, 57% other. Combining this with the results from our experiment, we get the following:
 
  Daily usage water Daily usage other
Shower gel 6.89g 8.96g
Soap 1.58g 3.80g

So, whether you're concerned about the water requirements, the chemical usage, or the transportation costs, of either product, it looks pretty clear that soap is the better option in all cases. It's hard to get any accurate idea of how they compare environmentally, but we can conclude that the reduced amounts of soap used in practice are unlikely to be outweighed by differences in the production process.

Of course, this is based on my own usage, and on a particular product line. Maybe it's different for you or for different products. Nevertheless, this has convinced me and I know which one I'll be sticking to in future.


 

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