SLS, mouth ulcers and the scientific method

Science isn't just something done by clever people in lab coats. The wonderful thing about the scientific method is that it can be done anywhere and by doing it, you can find out if something is really true. You don't have to believe hearsay or nod dumbly when the Big Wig tells you and everyone else what is true and what isn't true because That's What's Been Written. Instead, you can go away and find it out for yourself.

Another great thing about the scientific method is that it is relatively straightforward. Someone starts by having an idea about how an aspect of the world works. This is a person's possible theory or hypothesis (which literally means 'scene running beneath'). It is often the case that this hypothesis will fly in the face of the accepted theory. The person's hypothesis will often include assumptions about how the world works, which are its axioms. To find out if the hypothesis is true, a person will conduct several experiments. He or she designs these experiments to show, through physical events, whether or not the hypothesis is correct. Depending on the results, the person may conduct further experiments to make sure that the physical evidence he or she has gathered is proof that the hypothesis is correct and that there wasn't just a lucky coincidence, which would indicate a possible false correlation. Once false correlations are ruled out by isolating key elements, the hypothesis can be regarded as fact.

I carried out this process recently with a very mundane problem. I kept getting mouth ulcers. Mouth ulcers aren't fun. They're not life-threatening but they can be a real pain. On a regular basis, I'd been getting them since I was eight, or possibly earlier. About ten years ago, after a particularly bad infestation, I chatted about the problem to a colleague. He said with assured confidence that it was because I was eating acidic foods like tomatoes. I nodded in appreciation at this insight but later on, I thought 'my mouth should be perfectly able to eat tomatoes. Evolution would have weeded out such a simple problem'. But without any anything else to go on, I couldn't come up with a different hypothesis.

That is until last year, when I was chatting to friend. She remarked that she bought SLS-free soap for her young son because he'd had eczema problems since he was a baby. That got me thinking. 'My mouth ulcers are a skin problem of a kind. Could they be the result of my mouth being sensitive to SLS?' That idea became my hypothesis.

My next step was to investigate SLS. Sodium Lauryl Sulphate (or Laureth Sulphate or SLES if it's the 'ethyl' version) is a foaming agent. If you add a small amount of SLS to a product it makes the product foam up in an attractive manner as soon as you add water. Because of this, SLS is added to soaps, washing-up liquids and toothpaste, among others. It's in a lot of products. I noticed that it was in toothpaste. I checked my popular brand toothpaste; yep, it was an ingredient. My hypothesis that SLS was giving me mouth ulcers was still possible.

My next step was to perform an experiment; I stopped using my SLS toothpaste. I looked for an alternative brand, free of that ingredient. After a bit of effort, I found one in the local health food shop. I began using that toothpaste exclusively. After several weeks, I realised that I had not had a single mouth ulcer. It looked as if I had proved my hypothesis.

But then I thought: 'perhaps there is another ingredient in the toothpaste I was using previously that is really the cause of my mouth ulcers?' If that was true, then I would have had a false correlation. To test this possibility, I put some soap, containing SLS, on my fingers and then rubbed my fingers around the inside of my mouth. This way, I was isolating SLS from the other toothpaste ingredients. Twenty-four hours later, I had two painful, sensitive mouth ulcers. This experiment gave me the confidence to decide that SLS was the culprit. [There was still the possibility that some other ingredient was the actual culprit but I wasn't going to buy a hundred products and deliberately give myself mouth ulcers for two months. No way!]

Flushed with success (but not inflamed), I wondered about another skin problem I've had most of my life; clammy hands. Did SLS cause that too? That was a trickier challenge because we generally touch more chemical products with our hands than we put inside our mouths. To test this hypothesis, I had to get rid of SLS soaps (which includes pretty much all liquid soaps) and SLS washing up liquids, since I hand-washed my dishes. Eventually, I found an SLS free washing-up liquid made by 'earth friendly products'. Three weeks after switching to those products, I found that in my home at least, my hands were dry as a bone with almost no outbreaks of clamminess.

One day soon after, I popped around to chat to a neighbour. He handed me a mug for my tea, fresh from his kitchen draining-board and as I grasped it, my right hand broke out in a sweat. It was that fast! Not only that, but there couldn't have been much more than a tiny residue of SLS on the mug. Such a large reaction to such a small residue seems to indicate that my hands are hyper-sensitive to the chemical in a similar way to someone with an acute allergy. It was a fascinating reminder of how fast my hands would become clammy again if I let cheaper, SLS-based products back into my daily life.

Since that time, my mouth has been completely ulcer-free and my hands have been almost entirely bone-dry at home. Success!

p.s. If you've found this article interesting, you might want to read my article about Mono-Amine Oxidase, Preserved Meat and a child's Problem Behaviour.