system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between the types of radiation that cause cancer and the types of radiation used to treat cancer?
gpt
Below a certain intensity, ionizing radiation will damage your cells. Above a certain intensity, it will kill them. Damaged cells can mutate and become cancerous, which is why low-level, long-term irradiation from (for example) tanning beds or radioactive material poses such a threat.

When radiation is used to treat cancer, it is actually being used to *kill* the cancerous cells in your body - they are living tissue, and can't multiply if they're dead. In this case, the radiation will be at a very high dose and directed to a very specific area so that it will cause as little damage to the surrounding healthy tissue as possible.