Nettles are something to check out first, before making it part of a scene. I've made it personal policy never to do anything to my sub or use anything on my sub I haven't tried --- or I won't know what to expect.
In my case, the sting (after leaving 4 hours in contact) lasted more than 5 days. It does diminsh, but you know it's there. Worked with sub to try it, and she had an AWFUL allergic reaction. Darn near didn't make it; her throat was so swollen she could hardly breathe.
Just a brushing contact on the skin didn't seem to be really serious, and only lasted a short while. Longer contact was quite extreme.
I might write about it as a fantasy, but it stays out of the playroom!