Nettle Rash is the common (non-medical) name for the type of skin lesion also known as a wheal that can result from contact with plants commonly known as "nettles" or "stinging nettles" (e.g. Urtica dioica and others in the genus Urtica) or another allergen that results in a similar rash on those affected by it. See also the related glossary entry about the homeopathic remedy Urtica urens which is derived from a plant of this genus.
Generally, nettle rash takes the form of many round-shaped or flat-topped elevated lesions caused by flares of swollen skin containing an accumulation of fluid. (The medical term for "swollen with an excessive accumulation of fluid" is "edematous", although that word is not always used in medical textbooks).
Although usually transitory nettle rash can be a medical emergency if the lips, eyes, or tongue are affected because considerable swelling can occur.