N.B., The references to Aqueous Cream BP in this post are specific to the UK and those Commonwealth countries that use the BP. But I hope you will still find it interesting if you live elsewhere.
Many years ago I read a paper that changed my attitude to skin creams. It looked at the effect of cream base on peoples skin over time. It found that although the cream was moisturising in the short term, over the long term it reduced the skin’s barrier properties. So can a moisturiser thin your skin?
Despite reading it several times and thinking deeply about the implications, rather annoyingly I managed to misplace the actual paper. This was back in the days before the internet – it really is a boon being able to store things electronically. The paper had been bought as a photocopy from the British Museum and passed onto me via several hands. Having lost it I couldn’t remember the authors’ names, the title or even the journal it was published in, though it may very well have been Acta Dermato-Venereologica and probably came out in the nineties. And the work was done in Scandanavia.
If anyone recognises it from that description I would love to have the reference. You will be reuniting me with a long lost friend.
It just reported the observation and did not investigate why this should be the case. But I think I have a good idea of what might have been going on. This was brought back to the front of my mind by recent coverage of a similar but smaller bit of work done in Bath last year. This only involved six people but it confirmed what the Scandanavians had been saying. What they found was that applying Aqueous Cream BP had a tendency to make the skin a bit thinner and a bit drier when used repeatedly.
First of all, what is Aqueous Cream BP? The BP stands for British Pharmacopoeia. This is a compendium of basic pharmaceutical preparations and materials. If you see BP after the name of a material in the chemist it just means that it complies with the official specification laid down in the British Pharmacopoeia. Most of the entries are raw materials or actives, but there are a few preparations like this one. It can be used as a moisturiser on its own or as a base to apply actives to the skin. This saves every pharmacist from having to concoct their own recipe when the need for a skin cream arises.
The drawback is that the formulation doesn’t get updated very often. Looking at it today it looks really old fashioned. The Bath study got picked up on by the media when it came out. One thing that got commented on was that the cream used contained sodium lauryl sulphate, which is a known irritant.
This is true enough, sodium lauryl sulphate is not only a known irritant, it’s irritancy is so well known that it used as a reference irritant. If you want to assess just how irritating to the skin something is you compare it with sodium lauryl sulphate.
So what is a known irritant doing in a medical cream? Well it probably wouldn’t be if you were drawing up the pharmacopoeia today. There are some much milder alternatives around. But even so, just because something is irritant when it is used neat doesn’t necessarily mean it will be irritant when you blend it with other things. Aqueous Cream BP can irritate a few people, but most people don’t have a problem with it. And it wasn’t irritation that was found in this study, it was skin thinning and dehydration. These aren’t the same thing.
So let me tell you what I think is actually going on. Sodium lauryl sulphate doesn’t just cause skin irritation. It also interferes with the activity of an enzyme found right at the top layer of the skin called stratum corneum chymotryptic enzyme. The role of this enzyme is to regulate the speed at which the skin exfoliates itself, a process that sees cells continuously being lost from the surface of the skin.
So that is interesting. There is an ingredient in Aqueous Cream BP that directly affects a process that in turn has an effect on skin thickness.
As I say, the irritancy of sodium lauryl sulphate is well known. But it is also pretty well known that you can overcome that irritancy in a particular formulation. I won’t go into the details here – I have to keep something back for future blog posts – but just because you see sodium lauryl sulphate on an ingredient list don’t automatically assume that the product is going to irritate your skin. It is more likely that the person who came up with the formulation has taken that into account.
But the longer term effect on the skin is much less well known. In fact I have only seen a couple of papers about it. Thin skin is going to be drier than normal skin, so it is not something you want to pay good money to do to yourself. If you are at all inclined to dry skin I would definitely avoid Aqueous Cream BP and think about steering clear of products that contain sodium lauryl sulphate.
I don’t think Aqueous Cream BP is used much, but I have seen people on money saving forums pointing out that it is a cheap alternative to a more regular moisturiser. This is sort of true. If you have never heard of it and despite my warnings want to give it a try, ask for it at the counter in your local chemists. The last time I bought some I think I paid about £5 for a kilogram, so it is really cheap.
But there is another thing – the precise mechanism by which aqueous cream thins the skin isn’t known. But if I am right, I have a feeling it will turn out to be something that other ingredients with similar chemistry to sodium lauryl sulphate will do as well. So other formulations might well show the same behaviour even if they have different ingredients.
If you are a regular user of moisturising cream, my advice is to bear in mind that it might be doing good in the short run, but not necessarily in the long run. Try stopping using it for a few days on one part of your skin. If you find that your skin starts off by being very dry but seems to recover before you start moisturising again, maybe it is time to switch brands.
This study got quite a lot of coverage in the UK media late last year. The angle most of them concentrated on was the possibility that Aqueous Cream might make eczema worse. This might well turn out to be true, but as this write up from the NHS makes clear, it is far from proven.