When an atom loses an electron the molecule to which it belongs is left with an electrical charge. Ions react chemically with molecules in living cells causing mutations which result in cancer and immune deficiencies. Alpha particles carry a positive charge and travel no more than 40 millimetres through air. They penetrate the body to just below the dead skin. When released inside our bodies from material we breathe or swallow, alpha rays are able to transfer their energy at short range to damage body cells.
Beta rays are especially dangerous when emitted inside the body.
Early History Evidence of harm from radioactivity came soon after Marie and Pierre Curie discovered radium in 1898. They found radium reddened their skin as if from a burn. The burns were recognised as identical with those received by radiologists using X-rays. Radium began to be used to destroy cancer cells in the same way as X-rays. Despite the dangers, doctors injected radium into patients as a cure for almost every ailment from rheumatism to heart disease to cancer.