Diseases are crazy. If anyone's interest is piqued, read up on how the human immune system works to fight bacterial and viral infections. It is a system that rivals any war strategy on the battlefield. Absolutely an amazing thing.
Then, read up on how certain bacteria (e.g., E. coli O157) or viruses (e.g., HIV, Hepatitis, Herpes) have evolved to defeat our immune system. It's really a humbling experience.
And then, there's even these crazy malformed proteins, called prions, that can cause your brain to form wormlike holes (like a sponge) and insure your early death. This is the incurable Bovine Spongiform Encephalopathy, or Mad Cow Disease.
I certainly don't advocate living in a bubble (in fact, parents that have been too careful protecting their babies from germs may have inadvertently given their children allergies...). It is important to be exposed to germs to keep your immune system up to date and properly conditioned. However, being exposed to one of the really bad germs is bad.
(By the way, an allergy is a malfunction in your immune system; your immune system is tricked into thinking a harmless particle (like pollen) is a pathogen. The discomforts you feel are the side effects of your immune system waging war against this harmless particle.)