If the radioactive source is outside the body 1  : Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body. 2  Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside. Alpha radiation is the most dangerous because it is easily absorbed by cells. 2  Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it.