Science Questions

Will my skin soak up the calories in skin cream?

Sun, 15th Apr 2012

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Heather asked:

Whilst enjoying a regular podcast of NS in Ontario, Canada, I slather on oil-based face cream to keep my winter-weather-beaten face moisturised. Is there an absorption of calories to my daily count, I wonder?


Your programme has taught me heaps. Thanks.






We put this question to Richard Guy, Professor of Pharmaceutical Sciences at the University of Bath...

Given that a normal sized person, a grown up person, has a skin surface area of maybe 2 square metres and given that we’re about 70% made up of water on the inside, we would lose a lot of water across the skin if it didn’t perform efficiently as a protected barrier.  

Cold creamIt carries out this remarkable feat primarily through a very thin specialised layer, the stratum corneum.  This layer on most parts of the body is only 1/100th mm thick.  Under the microscope, stratum corneum looks a little bit like a brick wall.  The bricks are the skin cells. All the bricks can take out water, the lipids filling the spaces between them provide an oily film into which water transfers reluctantly.  Remember that old adage that water and oil don't mix.  

So, what happens when we apply oil-based creams to our face to provide some moisturisation during cold dry winters?  Is the oil or fat in the cream absorbed into the body making us put on weight?  Well, the short answer is no.  Not to any extent that you would notice around your waistline.   The function of the oily part of moisturising creams is to reinforce the lipids in the stratum corneum and to make it even more difficult for water escape.  

But where do the oils of the fats go in the end?  Well, they mix in with the natural lipids of the stratum corneum and some may well move gradually into the deeper layers of this thin barrier.  But once on the other side, they encounter an environment which is very watery.  In oily substance, this is not an attractive place and therefore, fat transfer out of the stratum corneum will be very slow and unfavourable. 

As a result, the amount of oils in the cream that will end up reaching the inside of the body will be very low.


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Apparently it does occur in premature babies ... RD, Wed, 4th Apr 2012

In adults, the effect would be small:
- Skin surface area is smaller relative to volume, compared to children
- The layer of dead cells on the skin would reduce absorption of oils into the skin layer
- The skin does not have all the enzymes and pH conditions that the gut has to metabolise oils and fats. evan_au, Fri, 6th Apr 2012

can deliver lipids intravenously ...

i.e. the oil just has to make it into the bloodstream. RD, Fri, 6th Apr 2012

I spoke with Prof Richard Guy at Bath University about this and he comments:

"Babies born prematurely have two important characteristics: (a) they are pretty small and, as you say, they have a high surface area to volume ratio, and (b) they have incompletely formed stratum corneum - that is, their skin barrier is not fully developed.  The reason for the latter is self-evident: in the womb, the baby is basically submerged in a water bath and is in no need of a barrier to water loss.  As the gestational period comes to its conclusion, however, and the foetus prepares for birth, the differentiation of the epidermis steps up a gear to generate a proper stratum corneum such that, on "popping out", the newborn has a skin barrier that's not much different from that of a healthy adult.

It's well-established in the literature and in clinical practice that premature babies have to be carefully monitored and maintained in well-controlled conditions, in particular, to stop excessive water loss across their skin.  Once has to be careful too with exposure to exogenous substances which may easily cross the less-than-fully-developed skin and cause potentially harmful effects.  The observation that rubbing oil on premature neonatal skin results in the appearance of some constituents in the blood is not too surprising therefore.  It's probable that the oil is also enhancing the weak skin barrier function in these babies and this will, in turn, improve their well-being.

Normal skin turnover means that we lose, on average, about one cell layer a day and that we always have a final layer of cells about to fall off the body.  However, with the exception of certain disease states where these layers of finally desquamating cells are not shed correctly, we do not build up large amounts of dead cells on the surface.  Further, when we apply lotions or creams, etc., the massaging in of the formulation almost certainly rubs off those soon-to-be-lost dead cells and they pose no really effective barrier to the uptake of material, therefore.

The skin and gut have completely different functions, of course.  The gut has evolved to be a an efficient mechanism by which we absorb nutrients from food and the pH, enzyme content, structure, and so on are highly developed to make this work.  This includes the absorption of fat which, at least in days gone by, was rather important in keeping Homo Sapiens alive.  In contrast, the skin has evolved to be a barrier, as described in my original response, and has no absorptive role in terms of keeping the organism alive.  As a result, it does not possess all those things which makes the gut so good at turning food into the building blocks that we need for life.

As an aside, though, it's fun to point out that the external skin and the gut (and by gut I would mean from the mouth to the anus) form a continuous, essentially uninterrupted surface, the functions of which are really distinct depending on where you are!

Hope that helps.  Best wishes,  R"

Thanks for your comments all!, Hannah nakedhannah, Mon, 16th Apr 2012

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