In general, most sea urchins only cause injuries through their spines. The spines easily penetrate the skin, especially when stepped on, break off and remain stuck in the skin as they are barbed. They often crumble when you try to remove them. Some sea urchin species have toxins inside their spines that can cause burning and itching at the entry points. In very rare cases, systemic toxin reactions (urticaria, headaches, vomiting, diarrhea) are possible.
Spines that have penetrated the skin, e.g. in the sole of the foot or at other contact points, must be removed individually. Particularly deep-seated spines can only be removed microinvasively. Remaining spines cause local infections in the skin, as well as persistent foreign body granulomas, which may need to be surgically removed. This is particularly the case if they have penetrated joints (risk of stiffening).
Contact with the short spines of leathery sea urchins (Asthenosoma species) hardly leads to visible injuries, but is extremely painful, although the pain subsides after 30 minutes.
Injuries caused by the grasping pincers of poisonous sea urchins (Toxopneustes species) are also extremely painful, although the pain subsides after 30 minutes. In individual cases, symptoms of poisoning may occur.
Contact with the up to 6 cm long spines of the crown-of-thorns starfish (Acanthaster planci) can lead to extremely painful injuries. Remains of the spines can be visualized radiologically and must be removed surgically.
Caution: Primin-containing sea urchins: Possible allergic reactions, cross-reactions, see cup primrose