Is there some sort of chemical in stinging nettles that make them sting you? And when they do sting you, why does it

Question: Is there some sort of chemical in stinging nettles that make them sting you? And when they do sting you, why does it make your skin itch and form a sort of lump?
- Keywords:
  stinging nettles
Asked by cookieland to Vera, Ed on 20 Jun 2011.
- Ed Morrison answered on 20 Jun 2011:
  
  Yes, when you get stung the nettle injects chemicals into you that cause the pain. I guess this is because they don’t want animals to trample on them. Your hands itches because you get a sort of allergic reaction to the chemicals. This is your body trynig to protect itself against harmful things in the environment – the swelling helps blood vessles to deliver more blood cells to fight any infection.
  
  Interestingly, gorillas don’t seem to mind stinging nettles and will chomp away on them quite happily!
- Vera Weisbecker answered on 20 Jun 2011:
  
  I didn’t know about the Gorillas! Nettles are really mean creatures – they have these little stinging-cells which, when you break their tip, release the stinging stuff on your skin. But like Ed I’m not sure what the exact compound is.

Question: Is there some sort of chemical in stinging nettles that make them sting you? And when they do sting you, why does it make your skin itch and form a sort of lump?