The detergent question: the results!

Back in May last year, the Nappy Science Gang citizen scientists decided we wanted to know what the best thing to wash cloth nappies was. Now, after many months designing experiments, testing detergents and many, many loads of washing, the results are finally in!

Our gang of cloth nappy users wanted find scientific answers to questions about cloth nappies, but had found that the science that was out there didn’t ask any of the questions that were relevant to us. So, the Nappy Science Gang set out to answer them – beginning with what washing agent is really best for cloth nappies. After many weeks of discussion and consultation with several soap, fabric and water experts, we designed and carried out a blind randomized test of seven washing agents, including bio and non-bio, liquids and powders as well as eco alternatives to find which which one was really the best.

Pictures taken by volunteers at various points during their experiments.

The experiment: What we did

The idea behind the experiment was simple – try out the seven washing agents (Sainsbury’s bio and non-bio washing powder, Sainsbury’s non-bio liquid tablets, Ecoegg, Soapnuts, Totsbots Potion and Sainsbury’s non-bio powder + Miofresh sanitiser) for a variety of water harnesses and see which one got the nappies cleanest.

So, 35 volunteers received packages of mystery washing agents which they used to wash three loads of their washing, before scoring the nappies on how they looked, felt and smelt and sending off a swab to the lab to see how many bacteria were left on the nappies. Confederates (aka, husbands, children or anyone else who was about) were involved too – they put the agents in the washing machine so the test was as blind as possible, and extra washes were done before each experiment to clear out any previous detergent.

Bacteria colonies grown on agar in a petri dish from the swabs of the test nappies. Each colony tells us that at least one live bacteria was present, as the dead bacteria won’t grow into colonies.

Unfortunately not all volunteers were able to complete all the experiments due to other commitments, and the plan to have empty eco eggs in all the washes so the bumping sound didn’t give away when the eco egg was being used was foiled by a incorrect packaging of the experiment packs. Some of the swabs were lost in the post too, but the hard work of all the volunteers meant that we managed to work these things out as we went along and still test each detergent a minimum of nine times.

You can see the full protocol along with full details of any changes here.

The results: What we found

After many long weeks testing, swabbing and sniffing, the results were collected and this is what we found. If you took part in the experiment, and have been wanting to know what you tested, here’s what each mystery detergent/washing agent was:-

A = Sainsbury’s bio powder
B = Sainsbury’s non-bio powder
C = Sainsbury’s non-bio liquid tablets
D = Ecoegg
E = Soapnuts
F = Totsbots Potion
G = Sainsbury’s non-bio powder + Miofresh sanitiser

So, how did they all score? First off, for participant scoring of the results, we can see from the graph below that Sainsbury’s bio powder pipped the other washing agents to the post, and soapnuts performed the worst by far.

washing agent score

Graph showing participant scores for the various washing agents tested.

Looking a bit closer at the scores split up by test, we can see that the eco egg’s score was based mostly on it’s feel, the bio powder rested mostly on it’s look and the non-bio +sanitiser was mostly on it’s smell.

Detergent Smell Look Feel Aggregate score

Sainsbury’s bio powder

3.8 4 3.6 3.8

Sainsbury’s non-bio powder

3.4 3.5 3.8 3.6

Sainsbury’s non-bio liquid tablets

3.5 3.6 3.4 3.5


3.2 3.3 4.1 3.5


2.8 2.2 3.2 2.7

Totsbots Potion

3.5 3.6 3.4 3.5

Sainsbury’s non-bio powder + Miofresh sanitiser

4.2 3.2 3.7 3.7

Table of average score for each washing agent on each of the tests performed.

However, if we take a look at the bacteria levels tested from the swabs people sent in, they seem to tell a slightly different story. Sainsbury’s non-bio powder + miofresh sanitiser did by far the best, the Eco-Egg did the worst for killing pathogenic bacteria and Sainsbury’s non-bio liquid did worst for killing bacteria overall. Pathogenic bacteria are more likely to cause diseases and are mostly from the gut, which means in terms of nappies these are the most important ones!

washing agent lab

Graph showing the bacteria coverage for the different washing agents tested.

However, although the participant scoring and the lab tests didn’t agree on an outright winner, there was definitely some common ground. Bio and non-bio powders (well, the ones we tested did, which we are hoping are failry representative of bios/non-bios in general as we can’t test all the detergents on the market!) did well on both tests, and liquidtablets, eco egg and soapnuts doing the less well on both tests, with soapnuts being the worst for participant scoring and second worst in the bacteria counts.

We all had plenty of thoughts on why this might have been. Taking a look at the raw data for the colony counts, we can see that there are lots of swabs which had no live bacteria on them at all, and indeed the Sainsbury’s non-bio powder + miofresh sanitiser had no colony counts at all! Dani who did the lab testing thought this could have been caused by swabbing not being carried out correctly, or the bacteria died from a low temperature in the post office. We also have to consider that many machines don’t reach the temperature specified which could have affected the colony counts as much as the detergent used.

It’s also worth noting that all our results are very clustered together and don’t show a whole lot of differentiation. This means that we’d need to do more testing, with more repeat trials for each type of detergent, to pin down the best detergent once and for all. The results we have though are certainly enough to provide plenty of food for thought in the meantime though!

In summary:

  • Bio and non-bio powders did well for bacteria levels and participant scoring
  • Liquidtablets and the Eco egg did less well on both tests
  • Soapnuts did the worst for participant scoring and second worst in the bacteria counts.
  • Another experiment with more trials and a better way of transporting swabs so the bacteria don’t die would help us get closer to a final answer on the best detergent.