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Soaps are amphiphilic molecules that, practically, removes body oils from the surface of the skin. The body, on the other hand, always replenishes sebum through the sebaceous glands after a certain amount of time.

Applying Le Chatelier's principle to this complex chemical equilibrium, where the equilibrium shifts towards the right hand side, where oil is being extracted from the equation, essentially so:

(body · oil)  ⇌  body + oil       # RHS preferred

Because the process of sebum regeneration must be endothermic, this means the body is losing energy in this overall process:

body + (lipids + heat)  ⇌  body + oil  ⇌  (body · oil)

My questions are:

  • Are my assumptions correct?
  • Does removing oil from the body more readily, by means of a stronger detergent/soap, reduce body mass?
  • Does the temperature of the water bath used in the experiment affect the rate of sebum dissociation?
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    $\begingroup$ Haha, I have to say this is some original thinking, I like it! I suspect this won't happen because bodily functions tend to have strict kinetic controls (both reactional and diffusional) alongside thermodynamic ones, and so your "equilibrium" wouldn't shift so freely; perhaps sebacious glands are always working at essentially full throttle. If you don't find a satisfactory answer here, perhaps the question can be moved to Biology.SE, as the mechanism by which sebum is produced is likely important. $\endgroup$
    – Nicolau Saker Neto
    Commented Jan 3, 2014 at 16:29
  • $\begingroup$ You may be correct in principle but wrong that the amount could be significant. The issue isn't whether this effect happens but whether it could possibly be large enough to be even measurable in the real world where you weight fluctuates significantly hour by hour according to what you eat and the amount you sweat or excrete. $\endgroup$
    – matt_black
    Commented Jan 3, 2014 at 17:00
  • $\begingroup$ @matt_black Oh no, I am in no way concerned about its efficacy or practicality (it ruins your skin, for example), and do not encourage anyone bathing in laundry detergent -- just whether or not my thought experiment is on the right track. $\endgroup$
    – Brian
    Commented Jan 3, 2014 at 17:03
  • $\begingroup$ I find your assumption that the body will just get some fat out of existing storage to use in sebum production highly amusing. The amount of fat in fatty tissue is regulated by complex hormonal systems and is not just a "dumb storage" for excess calories. For all we know, it could be that the need for fat on the skin kicks the fat-demanding hormones into higher gear, creating more fat than before. So without knowing how fat is made (and I doubt the relationship you mentioned has been studied yet), any relation is possible. $\endgroup$
    – rumtscho
    Commented Feb 6, 2014 at 23:34

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I'm afraid no: you are applying a chemical principle to a complex biological response.

The Le Chatelier principle state:

If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.

We start with the definition of chemical system at equilibrium :

the temperature dependent condition in which chemical species are present at concentrations which have no further tendency to change with time.

So what you need are chemical species: molecules, ions. Although fatty acids could be a product "body" is not a compound or a molecule. So what you have is not a chemical system but a biological one. You could go a little more close if you think something like this: $$\ce{Fatty acid <=> Chemical \space Precursor_{Y} + Chemical \space Percursor_{X}}$$

However even this is a wrong oversimplification of many complex biochemistry reactions and equilibria.

Moreover you can't interact with these equilibria, perturbing them and so applying LC principle because sebum, which is a complex mixture of lipids, is stored inside sebaceous glands and is formed by the complete disintegration of the cell it self. So to from new sebum you have to from new sebaceous glands. Soap simply remove sebum not seabaceous glands, so using stronger soap by the way don't affect sebum production. At this point is clear that is no more chemistry but physiology. In this case an equivalent of Le Chatelier's principle is the homeostasis. However from what I know the diet is one of the main factors that induce sebaceous glands to produce sebum so eat better seems to be the best way to lose weight and sebum!

References

Pub Med Sebaceous gland lipids

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