Everyone in the post-nuclear world has some amount of radiation. Heck, if you live on a tall mountain, you will absorb some rads every year. And don't use those new fangled "Microwaves," as they can be very bad for your health. When you start the game, you will have very little to no measurable radiation. You can still encounter freak areas of radiation, but you are more likely to run into radiation-infected creatures that mean to do you harm. The more accumulated radiation damage you have, the worse the effect of additional radiation on your body. Since radiation damage takes a while to truly affect you, you would be wise to monitor this characteristic. You can tell exactly how much radiation you have been exposed to by using a Geiger counter. Some doctors may be able to treat radiation damage, and there are two types of drugs that can help.