Chicken pox is caused the the Varicella-Zoster virus, which attacks your respiratory system and presents in the form of a fever, then with fluid-filled, itchy vesicles (spots) all over your body. The virus is pretty easy to fight off for most children, so it's good if they're exposed at a relatively early age.
It's true that if you get chicken pox, you'll probably never catch it again. But it's not certain. Once you get it, your body "remembers" it and maintains the antiviruses it needs to fight it again for a long time. If you're exposed to it occasionally over your life, then you'll never catch it again because your body will fight it off before you even know it's there. But if you catch it once when you're small, and then never get exposed to it again, your body will eventually lose the ability to fight it off. Also, if your immune system is weakened by something like pregnancy or HIV/AIDS, you're more likely to catch it a second time.
The Varicella-Zoster virus doesn't always leave the body, either. It can become stored in your lymph nodes for years and years. Most frequently it re-surfaces in people over the age of 50 as Herpes Zoster, or shingles. Basically, it attacks various nerve groups and can cause extreme pain. These days, though, they offer booster vaccines for adults to make sure they don't get the disease. The downside is that insurance probably won't cover the cost of the vaccination.
It's true that if you get chicken pox, you'll probably never catch it again. But it's not certain. Once you get it, your body "remembers" it and maintains the antiviruses it needs to fight it again for a long time. If you're exposed to it occasionally over your life, then you'll never catch it again because your body will fight it off before you even know it's there. But if you catch it once when you're small, and then never get exposed to it again, your body will eventually lose the ability to fight it off. Also, if your immune system is weakened by something like pregnancy or HIV/AIDS, you're more likely to catch it a second time.
The Varicella-Zoster virus doesn't always leave the body, either. It can become stored in your lymph nodes for years and years. Most frequently it re-surfaces in people over the age of 50 as Herpes Zoster, or shingles. Basically, it attacks various nerve groups and can cause extreme pain. These days, though, they offer booster vaccines for adults to make sure they don't get the disease. The downside is that insurance probably won't cover the cost of the vaccination.