Source: Freepik
There are many types of radiation that are common throughout Earth, but only are specific to space. When launching astronauts to space, they are vulnerable to a few types of radiation such as galactic cosmic rays and solar particle events.
These types of radiation are harmful because it can increase the chance of cancer and diseases due to exposure for a significant amount of time. Additionally, cosmic rays are more dangerous than other types of radiation because they are ionizing, rather than other forms of radiation that are non-ionizing like infrared radiation or microwave radiation.
As ionizing radiation is associated with high energy, meaning that it results in a more positively charged atom which can potentially alter substances and permanently damage them.
Galatic Cosmic Rays originate from outside of our solar system, but they travel near the speed of light and can go through most materials and the flesh of humans. This is especially damaging to astronauts because the radiation can target the spacecraft that is launched from Earth and ultimately cause diseases that could end the life of the astronauts.
The reason why radiation is especially damaging to astronauts is because Earth has a magnetic field that protects us from major ionizing radiation types and even some solar flares from the Sun, but as astronauts leave Earth they no longer get the protection they need.
Thankfully, the astronauts get suits that can protect them from many types of radiation, but not all radiation is protected. Allowing contact to space radiation can potentially leave long-term effects, but in the history of space travel it did not lead to any deaths.
References
NASA. (2023, April 27). Why space radiation matters. NASA. http://www.nasa.gov/missions/analog-field-testing/why-space-radiation-matters/