In medicine, urtication, or flogging with nettles, is the process of deliberately applying stinging nettles to the skin in order to provoke inflammation or rash. An agent thus used is known as a rubefacient (i.e. something that causes redness). This is done as a folk remedy for rheumatism, as it provides temporary relief from pain.
Urtication is also performed by BDSM practitioners who use stinging nettles for sexual stimulation.
In the flash movie Salad Fingers, the main character finds it exceedingly pleasurable to urticate himself, especially with nettles. He uses the nettles to "make the milk drop out from inside [his] 'teat'."