Okay, you’ve got really dry skin. What is a good choice of skin cream? One approach is to look for actives that have a good effect and then find a product that has a lot of that ingredient. This sounds good in theory but it isn’t always easy to work out which of the many active ingredients the adverts are shouting about actually work. And it is almost impossible to work out how much of those ingredients are in any given product. But it’s not impossible. Let’s have a look at Eucerin Extra Dry Skin Intensive 10% w/ w Urea Treatment Lotion.
Eucerin helpfully includes the fact that it contains 10% urea in big letters on the front of the box. And they make it clear that this is for dry skin by the most direct means possible. ‘Dry Skin’ it says. Plain speaking is rare and refreshing in the world of cosmetic promotion.
You can afford a direct and no thrills approach if you are selling something this straight forward. The only thing that is perhaps a little obscure for some people is the w/w after the 10%. This simply means the 10% is calculated on weight for weight basis. There is no significance of this whatever for users of this product. But as they have brought it up, it means that there are 10g of urea in 100g of product. The alternative is w/v or weight to volume which would mean 10g in 100ml. You can lead a happy and productive life not having to worry about this kind of thing, but it can be important to chemists. If you are a fan of the programme Breaking Bad you might remember that at one stage they rob a train of a chemical and replace it with water. Walter White might be morally ambiguous but he is a good enough chemist to adjust the amount they took for the different weight of the same volume of the chemical.
It was a slight detail that few people would have noticed, but it delighted me and I am sure many other morally ambiguous chemists around the world.
Eucerin emphasises its urea content because urea is a well known treatment for dry skin which has a long track record of success and which has been demonstrated clinically reasonably often. The beneficial effects of urea are well established and have been known for a long time. The Italian chemist Primo Levi describes how he hit on a great money making idea just after the war when work for scientists was in short supply. He realised that urea could be extracted from python excrement which is unusually rich in its precursor, uric acid. This could be lucrative because urea production facilities had been diverted to making explosives. Now things were getting back to normal there was bound to be great demand for cosmetics again.
Sadly, it came to nothing. When he got to Turin Zoo to enquire he was high-handedly told that the big pharmaceutical companies had already contracted to take away all the excrement the pythons could produce at a very high price. There was none to spare. Urea was that highly regarded.
It works by acting as a humectant much like glycerin. It is debatable whether it works any better, but there is one recent trial that suggests urea does indeed have a better moisturising benefit than glycerin. My opinion is that it is more a question of what suits your particular skin best. Urea is used for enhancing skin penetration in some pharmaceuticals – though the enhancement is fairly modest. This might mean that if your skin is both dry and sensitive, you might find using urea enhances your reaction to other things. And urea can be irritating at low pH. This won’t be an issue using Eucerin on its own, but conceivably the residual urea could become irritating if you were to subsequently use something like a hair conditioner. But these are pretty minor quibbles and most people most of the time are not going to have any problems with urea. As with other humectants, it will probably take a bit of practice to work out the dose that gives you the best results. Also, don’t expect any benefit if your skin isn’t dry to begin with. This product is all about solving a problem, and if you don’t have the problem it won’t do you any good.
So all in all a pretty good option to try if you are a dry skin sufferer.
Lodén, M., Andersson, A.-C., Andersson, C., Frödin, T., Öman, H. and Lindberg, M. (2001), Instrumental and dermatologist evaluation of the effect of glycerine and urea on dry skin in atopic dermatitis. Skin Research and Technology, 7: 209–213. doi: 10.1034/j.1600-0846.2001.70401.x