The outer layer of skin of a human is called the epidermis. It is supposed to be waterproof, however:

Using any current science and substances, would it be possible for humans to survive for two months purely by absorbing substances through the epidermis? The skin must not be pierced or otherwise physically damaged. (Prune skin does not count as damage)

There is no limit to how many hours per day it takes. The subjects lie completely submerged in a bath of nutrients with breathing apparatus. They can get in and out but must not use any other source of food or water.


The subjects are ordinary humans who are concerned about ageing. They have volunteered for an experiment. The crazy scientist has convinced them that if they stay there for two months (sedated to avoid claustrophobia but with VR glasses for entertainment) they will regain their youth. Assuming they can stand the discomfort, will they make it out alive or will they die or have to be rescued?

  • $\begingroup$ You still want them to be working humans and not mutans of crazy biologist? $\endgroup$ Commented Nov 20, 2018 at 19:31
  • $\begingroup$ See new info in the question. $\endgroup$ Commented Nov 20, 2018 at 19:40
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    $\begingroup$ Why not just feed them like coma patients: feeding tubes or injection into a vein? $\endgroup$ Commented Nov 20, 2018 at 19:41
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    $\begingroup$ Because the scientist is very knowledgeable but has gone completely nuts and is obsessed with this idea. By the way, academics have been known to get like this. I actually knew a highly qualified lecturer who started teaching his students complete nonsense and had to take medical leave in an institution. $\endgroup$ Commented Nov 20, 2018 at 19:53
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    $\begingroup$ Because the scientist knows that skin is not suited for nutrient + water absorbtion - why not plug in a nutrient hose rectally? no skin is damaged, might require some more sedation to get over the indignity, but that way nutrients land at least roughly where they are supposed to land. (Or why not do some feeding via a nasogastric tube? Doesn't pierce the skin either...) $\endgroup$
    – subrunner
    Commented Nov 21, 2018 at 10:25

3 Answers 3


Assuming they can stand the discomfort, will they make it out alive or will they die or have to be rescued?

They will starve.


Nutrients and water are absorbed in the intestine.

The average surface area of the human intestine is about $32 \ m^2$.

The average surface area of human skin is $1.5$ to $2.0 \ m^2$.

The average transit time in human intestine, from ingestion to expulsion, is about 50 hours.

This means that your subject will die of malnutrition, because they have 16 time less exchange surface to get their needed nutrients. To get the same amount of nutrients of a normal digestion they would need to bathe $16 \cdot 50 = 800 hours = 33 \ days$.

Death by starvation takes about that time, death by dehydration much less.

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    $\begingroup$ So no matter how concentrated and specially designed the nutrients so they don't need to be digested, they won't penetrate to the subcutaneous blood vessels? I'm not doubting, just asking $\endgroup$ Commented Nov 20, 2018 at 20:14
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    $\begingroup$ @chaslyfromUK, it not a matter of penetrating the skin. It's a matter of exchange surface. $\endgroup$
    – L.Dutch
    Commented Nov 20, 2018 at 20:14
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    $\begingroup$ In addition, skin isn't made to absorb food, so even if we had 32 m<sup>2</sup> of skin it wouldn't be easy. $\endgroup$
    – Ender Look
    Commented Nov 20, 2018 at 21:56
  • $\begingroup$ The logic is faulty. You need to factor in at minimum the daily requirement for 1 month survival (not "comfort") for each essential nutrient at minimum metabolic rates, and then identify for each, the optimal means to transport it or any precursor transdermally. That's a lot of ways to cut down the ratio. You also need to cut that 50 hours down - much of that time is used to preprocess food (break it down, or similar in stomach) or remove water, etc. (Cont) $\endgroup$
    – Stilez
    Commented Nov 20, 2018 at 23:39
  • $\begingroup$ The actual hours over which key nutrients are absorbed is much smaller, and in any case its probably a red herring and irrelevant anyway, because what counts is daily requirement not gut efficiency (how long the gut has to hold food to absorb from it). $\endgroup$
    – Stilez
    Commented Nov 20, 2018 at 23:40


The skin is a very specialized organ. Its job is litterally to be the first and greatest line of defense against the environement. It is what allows other organs to do their jobs without having to deal with for example dirt suddenly being on them. Afterall division of labor is what allows for specialization. So naturally it makes sense that skin is designed to block out as many substances as possible, like putrid water from a lake. Meanwhile other specialized structures are designed to allow the inteded entry of substances like a mouth.


Between the two options water is more plausibly absorbed by the skin. Problem is it cannot sustain life. Skin is designed to block substances as snall as the nano scale. Employing everything from fats and proteins to form such barriers. Water is a very small molecule so yes it can permeate these though at a slow rate.

The problem is the body expells excess heat and waste at great expense to its water supply. Thus it uses it faster than it can absorb it through the skin.


Utterly impossible. Some nutrients can permeate the skin. But food, the bulk majority of nutrients cannot. They are simply too large. More over most nutrients need to be converted in the intestine to be usable to the body, otherwise they would be out rigjt toxic.


In this situation we have two main thing to address: water and food.

  • Food.

    • They starve. Taken persons health, body mass, body fat, people can starve for 3-12 week, with some cases for 4-6 months.
    • As there is no info on this way of feeding, it is just a leap of thought. You could add keton bodies, maybe with ethanol ass addition.That will help them fuel ketosis.

    And yes, you can get drunk from bath in booze and die. Ketones do get absobed by skin. Just be carefull and not kill your patient, as too much is death.

    You can try adding glucose and BCAA. Note all that, most likely, wont be close to needed so you will be in starvation mode, but it will give you time and more comfort.

  • Water

    • Is water absorbtion from bath, assisted by ethanol, enough? More data needed. You can adjust air-supply so they loose less water, with sweat gone you can save close to 1 liter of water. Will you get 0.7-1.5 liters needed? Maybe.

In the end, if our mad scientist finds out, that his measures did not work. Just let them drink water and starve. Healthy with some body mass to lose will make it, weak with no spare body mass will die.

I will not volunteer for this one.

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    $\begingroup$ You can assume just about anything about transport systems through the skin as long as they are currently plausible science. Keton bodies and ethanol are fine by me if they'll keep the subject alive. If adjusting the proportion of gases in their air supply will help then by all means do it. $\endgroup$ Commented Nov 20, 2018 at 20:51
  • $\begingroup$ Just play with temperature and humidity, so you have less evaporation inside lungs. $\endgroup$ Commented Nov 20, 2018 at 20:54

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