Final answer:
Radiation is harmful because it can damage cells and DNA, create free radicals, cause genetic mutations, and increase the risk of cancer.
Step-by-step explanation:
Radiation is harmful to living things because it can cause damage to cells and DNA. The most harmful type of radiation is ionizing radiation, which can ionize molecules or break chemical bonds. This damages the molecule and disrupts cell processes. Radiation can also create free radicals, such as reactive hydroxyl radicals, that damage biological molecules and lead to genetic mutations. Furthermore, radiation can cause somatic or genetic damage, and can increase the risk of developing cancer in cells that are able to recover.