Formation of the Earth's Atmosphere. The early Earth was very different from our Earth today. The early Earth experienced frequent impacts from asteroids and meteorites and had much more frequent volcanic eruptions. There was no life on Earth for the first billion years because the atmosphere was not suitable for life.
Iron, oxygen and water react with the iron creating a substance known to us as rust.
Hope this helps.
Other reasons are
Not finishing the antibiotics.
Or
Taking antibiotics too often
In alimentary canal, food get digested by the action of many enzymes secreted by various glands including Liver, Pancreas and salivary glands....
The answer is carbohydrate.
