Radioactivity is dangerous because it can expose people to a harmful dose of radiation even without being aware of it. A number of small doses received over a very long time could lead to leukaemia or cancer in later life.
Radiation can lead to the retention of a potentially harmful amount of radium in one’s bones. Radioactivity resulting from nuclear bomb tests can cause ingenuous quantities of radiostronium and radiocaesium to get into food.
A radium compound was once used in the manufacture of luminous paint for the numbers on clocks, watches and instrument dials. The girls who painted these had a habit of putting the brush in their mouths to get a fine pointed tip. In those days the danger was not realized, and, over a long period, many workers absorbed enough radium to cause death in later years.