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?
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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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!
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.