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Why do we feel a burning sensation when water touches cuts/wounds? People suggest applying oil over cuts while bathing to prevent water touching it, but water is heavier than oil so it shouldn't work, but it does, Why?

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Water changes the local ionic concentrations and therefore induces an electric signal at exposed neuron membranes.Oil is used to prevent entrance of water to the cut because it is hydrophobic i.e. repels water but attaches to the tissue. Gravity plays no role here.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

  • $\begingroup$ why does gravity play no role $\endgroup$ – Ram Keswani Nov 12 '17 at 9:33
  • $\begingroup$ @RamKeswani Presumably because the force of adhesion between the oil and the skin is stronger than gravity, as is the force of the oil repelling the water. I'm no physicist, but that makes sense to me... ;-) $\endgroup$ – General Nuisance Nov 19 '17 at 18:13
  • $\begingroup$ Hi, welcome to Bio.SE! Please provide citations and appropriate forms of support for your answers. See our help page for further suggestions for writing good answers. Thanks! $\endgroup$ – theforestecologist Nov 20 '17 at 1:53
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It's a phenomenon called cutaneous hyperalgesia in which non-noxious stimulus like water cause pain. The Mechanism behind that phenomenon is the accumulation of pain-producing factors like (substance P), proteolytic enzymes, histamine or bradykinin which easily stimulate the nerve endings of the pain in the cut area. These substances are released from damaged cells. So the pain threshold is lowered. The non-painful stimuli become painful and the painful stimuli become exaggerated!

And sorry if I don't know about the oil and how it prevents that!

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  • $\begingroup$ Hi, welcome to Bio.SE! Please provide citations and appropriate forms of support for your answers. See our help page for further suggestions for writing good answers. Thanks! $\endgroup$ – theforestecologist Nov 20 '17 at 1:52
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Your nerves withold a solution that has an electrical charge, when water enters a damaged nerve and nerve membrane, it changes the electrical balance in the nerve. Wounds are supposed to be treated with physical cleaning and topical antisceptic.

Here is a more scientific account:

Cells normally have a functioning ion pumps. Cells are surrounded by a membrane that acts as a wall with little holes that ions(sodium,chloride,potassium, calcium) can pass through with difficulty. There pumps in functioning cells exchange of sodium, chloride and potassium. This causes a difference in electrical potential across the cell membrane, in effect making the cell a battery. By exposing that tissue to water, which has no sodium or chloride, you immediately changed the concentrations of these ions surrounding these injured pain cells causing them all to fire at once.

Cleaning is normally water and soap or saline solution (9mg/L approx). Non stinging antisceptics currently favored by doctors are Betadine, Merbromin, amonst others.

I like alcohol for reed cuts etc because it indicates when the exposed inner cell inside the cut and under the miasma have been well sterilized and attained.

https://www.quora.com/Why-do-wounds-hurt-more-when-they-get-wet

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  • $\begingroup$ Soap and water (S&W) is fine. The dirtier the wound, the more S&W. No serious medical professional recommends Betadine and water for wounds. It's used in hospitals because it's there/easier to use than soap, but even there, that's changing. (E.g. We used to irrigate wounds with normal saline under pressure. Now we use a faucet/tap water and a non-stinging soap and water. Both Betadine and alcohol are harmful (to some degree) to living cells. And soap and water is better than alcohol, which no doctor in their right mind would use for fear of being punched - and hard - by the patient. $\endgroup$ – anongoodnurse Oct 31 '17 at 20:18
  • $\begingroup$ Biologists often disagree on facts. I'm surpised that using antisceptic on wounds is a controversial practice, considering it's more likely to stop infection than water based treatments. We probably only disagree on my poor wording. $\endgroup$ – com.prehensible Nov 5 '17 at 14:35
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    $\begingroup$ @com.prehens.ible et al. please be nice to each other :) I am deleting most of this comment thread as this doesn't really seems to go anywhere. What I do know is that throwing youtube videos to a hardened veteran in healthcare won't really help. YouTube and Quora are no credible sources. I think anongoodnurse's issues arise mostly from the lack of references in your answer. If you guys prefer to have the thread migrated to chat, I'm happy to revive the comments and create a chat room. Cheers. $\endgroup$ – AliceD Nov 5 '17 at 20:06

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