Rust, on its own, is not harmful to one's health. According to the United States Environmental Protection Agency, ingesting rust from a water source does not present adverse health effects. Rust also doesn't cause tetanus, but stepping on a rusty nail might when one is not immunized to the disease.
The North Dakota Department of Health states that tetanus is caused by a bacterium and that any damage to the body or skin, even burns or blisters, may allow tetanus bacteria to enter the body. The Centers for Disease Control and Prevention also report that there is no evidence that inhaling rust or iron oxide dust can cause irreversible health damage.