Why doesn't soap or oil destroy your skin's epidermis?

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Summary:

Shouldn't an external environment consisting of oil or soap disrupt the cell membranes of the epidermis or other epithelial cells?

Main Question or Discussion Point

Cell membranes are made of a bilayer of amphiphilic phospholipids, where the lipophilic portions of the molecules face toward each other, and the hydrophilic portions face outwards towards the cytoplasm or the external cellular environment which is aqueous and therefore orients those phosopholipid molecules.

But then, what happens if you wash your hands with soap (a surfactant) or apply oil to your skin? Or brush your teeth where the oral mucosal epithelium of the mouth is exposed to a surfactant, or eat oily food? Or get soap in your eyes in the shower, with subsequent exposure of the conjunctival and corneal epithelium to a surfactant? All of a sudden, you no longer have a hydrophilic external environment to the cell membrane. You might then predict that all of these epithelial cell membranes would get disrupted and the cells would die and slough off. You would predict it would be chemically even more dangerous than an acid or alkali burn.

But that doesn't happen. Why not?
 

Answers and Replies

  • #2
pinball1970
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Summary: Shouldn't an external environment consisting of oil or soap disrupt the cell membranes of the epidermis or other epithelial cells?

Cell membranes are made of a bilayer of amphiphilic phospholipids, where the lipophilic portions of the molecules face toward each other, and the hydrophilic portions face outwards towards the cytoplasm or the external cellular environment which is aqueous and therefore orients those phosopholipid molecules.

But then, what happens if you wash your hands with soap (a surfactant) or apply oil to your skin? Or brush your teeth where the oral mucosal epithelium of the mouth is exposed to a surfactant, or eat oily food? Or get soap in your eyes in the shower, with subsequent exposure of the conjunctival and corneal epithelium to a surfactant? All of a sudden, you no longer have a hydrophilic external environment to the cell membrane. You might then predict that all of these epithelial cell membranes would get disrupted and the cells would die and slough off. You would predict it would be chemically even more dangerous than an acid or alkali burn.

But that doesn't happen. Why not?
Dirt and oil produced by subacious glands do come off in a emulsion with soap, your skin and hair become squeaky clean as there is now much more friction without the oil acting as a lubricant. The cells in our bodies however are strongly associated in functional tissues, they will not just yield their contents in water, surfactant or not. Dead and live epithelial cells will and do come off in certain tissues and these can be damaged by certain chemicals. Cells can be disrupted only if the chemistry of the environment is stronger electrostatically than the bonds in the tissues/ cells
A surfactant in washing up liquid will not do that although it will sting your eye due to inflammatory response.
 
  • #3
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Dirt and oil produced by subacious glands do come off in a emulsion with soap, your skin and hair become squeaky clean as there is now much more friction without the oil acting as a lubricant. The cells in our bodies however are strongly associated in functional tissues, they will not just yield their contents in water, surfactant or not. Dead and live epithelial cells will and do come off in certain tissues and these can be damaged by certain chemicals. Cells can be disrupted only if the chemistry of the environment is stronger electrostatically than the bonds in the tissues/ cells
A surfactant in washing up liquid will not do that although it will sting your eye due to inflammatory response.
I don't think the eyes stinging with soap is as much due to the surfactant as it is to the suboptimal pH and other chemicals in the soap/shampoo. For example, you can optimize those other things so that a surfactant like baby shampoo has no sting.

As far as "The cells in our bodies however are strongly associated in functional tissues, they will not just yield their contents in water, surfactant or not", I can understand this conceptually. Clearly, that is indeed what happens. But what I have trouble understanding is "why not?"

Thinking of it from a purely chemical standpoint, it makes no sense that that would not be a problem. What is it about cell membranes being strongly associated in functional tissues like epithelium that makes them so immune to disruption when their external environment is not hydrophilic? After all, these cells are directly exposed to the external environment, especially in non-keratinizing epithelium like the conjunctiva, mouth, or esophagus.
 
  • #4
DaveC426913
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Are we accounting for the dead (and dessicated) layer of epidermis that protects the live tissue?

(To apply some monitor leads, a technician once scrubbed my shin thoroughly. I remarked that he must have used some coloured disinfectant because that patch of my skin was now orange/yellow. He said No. That's actually what colour your skin is after scrubbing off the layer of dead tissue.)
 
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  • #5
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Are we accounting for the dead (and dessicated) layer of epidermis that protects the live tissue?

(To apply some monitor leads, a technician once scrubbed my shin thoroughly. I remarked that he must have used some coloured disinfectant because that patch of my skin was now orange/yellow. He said No. That's actually what colour your skin is after scrubbing off the layer of dead tissue.)
Yes. I think histologically, what people refer to as "dead skin" is just the superficial keratin layer on the epidermis. That exfoliates all the time spontaneously, and you can certainly scrub it off if you rub it enough. That might be some sort of explanation for the epidermis (although I would think that if you apply oils like vaseline or baby oil to the skin, you are going to get the oil to the surface epithelial layers anyway because the surface keratin layer absorbs the oil and will still expose the surface epidermal cells to them).

But that's why in the post above I was highlighting non-keratinizing epithelial layers, and how oil or soap don't disrupt those at all either.
 
  • #6
pinball1970
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I don't think the eyes stinging with soap is as much due to the surfactant as it is to the suboptimal pH and other chemicals in the soap/shampoo. For example, you can optimize those other things so that a surfactant like baby shampoo has no sting.

As far as "The cells in our bodies however are strongly associated in functional tissues, they will not just yield their contents in water, surfactant or not", I can understand this conceptually. Clearly, that is indeed what happens. But what I have trouble understanding is "why not?"
Cells have evolved this way to protect the functions inside and be malleable enough to allow cell division.
Have a look at the typical cell membrane then have a look at the sort of species that can disrupt it
 
  • #7
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Cells have evolved this way to protect the functions inside and be malleable enough to allow cell division.
Have a look at the typical cell membrane then have a look at the sort of species that can disrupt it
Yes I understand. I have no problem accepting THAT that it happens ( and I am glad it does ). My question is HOW? It makes no sense from a chemistry standpoint, based on what I understand of the explanations. There has to be some kind of explanation for the phenomenon.

It’s not an observation that the model would predict, at least from what I understand of it.
 
  • #8
pinball1970
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Yes I understand. I have no problem accepting THAT that it happens ( and I am glad it does ). My question is HOW? It makes no sense from a chemistry standpoint, based on what I understand of the explanations. There has to be some kind of explanation for the phenomenon.

It’s not an observation that the model would predict, at least from what I understand of it.
The integrity of the membrane is maintained by a plethora of structural proteins, fatty acids, glycolipids, cholesterol and the structure of the bi layer itself.

There strong bonds between these molecules and interaction with the external environment is regulated and maintained and there are strong bonds between these molecules which have to be overcome for the cell to be ruptured.



A surfactant is not strong enough electronically to disrupt that arrangement.



There is a section on surfactant “Dynamics of surfactants at interfaces” below which discusses the kinetic limitations and diffusion coefficient you may be referring to.



I am not a chemist (or cell biologist/biochemist!) so a more detailed explanation would be better coming from someone who has a better knowledge/understanding



https://en.wikipedia.org/wiki/Surfactant#Composition_and_structure
 
  • #9
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The integrity of the membrane is maintained by a plethora of structural proteins, fatty acids, glycolipids, cholesterol and the structure of the bi layer itself.

There strong bonds between these molecules and interaction with the external environment is regulated and maintained and there are strong bonds between these molecules which have to be overcome for the cell to be ruptured.



A surfactant is not strong enough electronically to disrupt that arrangement.



There is a section on surfactant “Dynamics of surfactants at interfaces” below which discusses the kinetic limitations and diffusion coefficient you may be referring to.



I am not a chemist (or cell biologist/biochemist!) so a more detailed explanation would be better coming from someone who has a better knowledge/understanding



https://en.wikipedia.org/wiki/Surfactant#Composition_and_structure
I see. Wow, those cell membrane hydrophobic/hydrophilic interactions must be pretty darn strong. Impressive. Thanks for the link!
 
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  • #11
DaveC426913
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The integrity of the membrane is maintained by a plethora of structural proteins, fatty acids, glycolipids, cholesterol and the structure of the bi layer itself.
Caution: the plethora is thin and easily abraded, so don't scrub too hard!
😄
 
  • #12
pinball1970
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Caution: the plethora is thin and easily abraded, so don't scrub too hard!
😄
Yes I read your post on that, that sounded painful!
 

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