Exposure of the skin: External exposure to alpha radiation is less of aproblem as it has a very short range (2 to 5 cm in air) and does not penetrate the skin (unless you have a cut). Beta radiation’s range is about 3 metres in air. Thin metal and/or personal protective equipment (PPE) is sufficient to lower exposure considerably. However, external exposure to gamma radiation does penetrate the body and cannot be stopped by PPE. Health impacts are dependent on the dose received and the length of time exposed.
Exposure of the internal organs: Another important route of exposure is when a radioactive element is swallowed or inhaled in the form of dust. In this case, alpha and beta radiation cause the most damage as their radioactivity affects the local cells. Inhaling Radon-222 gas can be very hazardous as it decays into other solid radioactive elements that emit alpha radiation. These stay lodged in the lungs. Even a very small amount of alpha radiation in the lungs has the potential to cause lung cancer.
The impact of radiation on your health depends on the type (alpha, beta, gamma), the organs of the body exposed (lungs, kidneys, skin, etc), the strength of the radiation (dose) and the amount of time that you are exposed for. For ease of assessment and comparison, these factors have been combined into a measure called the effective dose, reported in Sieverts, or more usually, millisieverts (mSv).