Friday, 19 June 2015 and Does rubbing a nettle sting with a dock leaf actually help? How? and are great sites for finding answers to technical questions on software and computers. Their aim is to have the correct (and up to date) answers for any question. Community voted and moderated. It really works well.

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Until now I never found a question that was not asked! have now been adding sites on a myriad of different topics like english, mathematics, bicycles, physics, parenting and health to name just a few. See a neat word/icon - cloud - map - thingy  here:

So my first question:
From a young age we were taught that the treatment for a nettle sting was to rub it with a dock leaf. Conveniently, docks usually grow close to where there are nettles.
  • Does this actually do something to help?
  • Is the effect entirely/mostly placebotic?
  • How does it work? (and what is the best technique to use?)
  • Would washing/rubbing with water be as/more effective?
As an adult if I get stung I have used the same treatment. It does seem to gradually calm the sting but it is difficult to say if the sting would be better without the treatment.
Psychological action? A bit of magic and a bit of placebo.
The treatment especially seems to help kids. Looking around for dock leaves is a great distraction. Kids are really happy to be able to help and do something about the problem. I have also heard that getting stung with a nettle is "lucky" (think magic fairy type of lucky here - woo!) and also that it gives a boost to the immune system (now that sounds much more scientific!). These two things are another good distraction and comfort to kids especially.
Physical action ?
Does rubbing the sting with juice of dock leaf simple rub away the sting needles? And does the juice dilute the chemicals injected in the sting?
In the summer when the nettles are out and it is common to get stung I have found several times that no water is convenient (even in Ireland) so the best source of something cooling is a crushed dock leaf.
Chemical action ?
I believed nettles had an acid in the sting and that dock leaves had a base. And a simple acid+base=>salt+water neturalising reaction took place to calm the sting.
However, reading a bit more about this shows up different and sometimes contradictory information. It is hard to determine what are actual facts. What chemicals are involved depend on what article you are reading!
I think the facts on nettle sting are: Stinging nettles have sharp needles of silica(glass). There is a mix of chemicals which are injected by the needles. From wikipedia : several chemicals: acetylcholine, histamine, 5-HT (serotonin), moroidin, leukotrienes, and possibly formic acid.
Doc leaves are related to sorrel (and related to rhubarb). The leaves contain oxalic acid and tannins. It is also said they contains an antihistamine.

Some more links / references / info . . .  The Chemistry of stinging nettles.
".I get severe raised whelps that hurt and last for two to three days...... unless I treat it pretty straight way with milk weed... I am not sure if that is the same as your Dock weed plant.. but I find it really takes the sting out.. bu it does not work for me if I delay treatment.  It needs to be done straight way.. with crushed milk weed juice...."
" The antihistamine from the dock leaf together with the natural healing properties of saliva will ease the stinging sensation."

"An astringent substance is a chemical compound that tends to shrink or constrict body tissues. The word "astringent" derives from Latin adstringere, meaning "to bind fast". Two common examples arecalamine lotion and witch hazel." 
"Astringency is also the dry, puckering mouthfeel caused by tannins found in many fruits such as blackthorn (sloe berries),Aronia chokeberry, chokecherrybird cherryquince and persimmon fruits, and banana skins. The tannins (which are types of polyphenols) bind the salivary proteins, causing them to precipitate or aggregate[2] and lead to a rough "sandpapery" or dry sensation in the mouth." 

Dock leaves ~= sorrel and stinging nettles as remedies:

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