Sea urchin spines can be venomous or cause infection. Granuloma and staining of the skin from the natural dye inside the sea urchin can also occur. Breathing problems may indicate a serious reaction to toxins in the sea urchin.
Following injury by a non-venomous sea urchin, the spine can stay for a while inside the flesh, causing pain and discomfort. The spines dissolve after a time, or are expelled from the body.