Stinging hairs of nettles are hollow, pointed cells with a tip made of pure silica, which breaks leaving a jagged point when you brush against it. The nettle sting contains irritants – mainly formic acid and histamines – that are injected into the surface layer of the skin cells.
It is often claimed that crushed dock leaves relieve the pain because their alkaline sap neutralises the nettle’s formic acid, but dock leaf sap is acid too, so this cannot be true. Nevertheless, many find that the dock leaf remedy seems to work, so there may be other reasons for this.
One is that dock leaf juice evaporating from the skin may have a surface cooling effect on the burning sensation. Another is that dock leaves might contain natural antihistamines that reduce the irritation, though none have been identified. The placebo effect, where faith in the efficacy of dock juice, might lower the perception of the sting symptoms, cannot be discounted either.
However, if you really want to neutralise the effect of the nettle sting’s acid, try treating it with soap, milk or a dilute solution of baking soda, which are all alkaline.
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