There are lots of ways to get sick, but there are two main reasons people get sick: The environment and their genes. Environment means what you do, where you live, where you go to school and work. For example, if you’re around people who have infectious disease (like colds) you’re more likely to get a cold. Genes are the blue print for your body. Some people have genes that give them a strong immune system that means they are less likely to get sick, other people have a weaker immune system so they have more problems fighting off disease.
There’s also disease that happen because the genes don’t work right. Some kids might be born with a heart that can pump correctly, or has small holes in it, for example. Genetic disease usually happens because of bad luck, there is nothing the kids (or parents) did to get it.