Stings of spiny sea urchin can 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, that help to dissolve the spine. Make sure that the spine or a part of it is completely removed from the skin. The spine could otherwise “move” inwards causing skin inflammation or nerve tissue injuries.