In what ways can harmful substances enter the human body?

There are many ways to catch a disease, get infected with some kind of virus, get poisoned, and so on. Let’s take a look at some of them:
1. Many viruses are transmitted by airborne droplets, such as chickenpox or herpes. Even a mask or a short distance does not help. Almost the entire population of the world is carriers of herpes.
2.due to a weakened immune system (for example, in the winter season), you can catch flu or ARVI
3. You can get poisoned if you eat some expired product. After the product expires, it becomes dangerous to humans, can cause intestinal infection and even death (dysentery).
4. You can get poisoned not only by food, but also by poisonous gases and fumes. For example, among the people living in the city, there are much more people with lung disease, asthmatics than in the mountains. When people smoke, they themselves poison their body.