Sea urchin’s spines can sting and cause pain and burning. Very often the spine breaks off into the skin.
What to do.
Wash the affected area with sea water or disinfectant and remove the spine with some tweezers. Apply several compresses of vinegar: this will help to dissolve the spine. Make sure that the spine or the splinter is completely removed from the skin. The spine could otherwise “move” inwards causing skin inflammation or nerve injuries.