Nearly everyone remembers their parents' warnings about rusty old nails, and some may have even been dragged to the doctor's office for a shot. As it turns out, rust doesn't actually cause tetanus.
What is tetanus?
Tetanus is caused by a bacteria called Clostridium tetani, which is commonly found in soil, dust and feces. Exposing an open wound to any object which has come into contact with the bacteria can cause tetanus, regardless of whether the object was rusty. Nails got their reputation as vehicles for tetanus partially because they can cause puncture wounds – the deeper the wound, the more likely you'll get an infection, because Clostridium tetani thrives in oxygen deprived settings like the one deep below the surface of your skin, according to Curiosity. Any injury from as small as a paper cut to a deep animal bite carries the potential for tetanus infection.
Tetanus, also known as lockjaw, causes extreme symptoms and sometimes even death. McGill University reports that tetanus is fatal in about 10% of cases. According to Curiosity, Clostridium tetani releases a powerful neurotoxin called tetanospasmin. This neurotoxin causes muscle stiffness and convulsive spasms that usually begin in the jaw, and is accompanied by fever and difficulty swallowing. To protect yourself, keep your immunizations up to date. Most people get a tetanus shot when they're young, but boosters can help prevent infection if you happen to be exposed to the bacteria as an adult.
If you end up with a tetanus infection, you'll need to go to a hospital for an antitoxin called tetanus immune globulin, since the spores of Clostridium tetani are resistant to antiseptics. It's important that you get to the hospital fast to catch the bacteria before they latch on to your nerve endings. HowStuffWorks says those who require treatment undergo a regimen of sedatives, muscle relaxers and occasionally surgery.
How the rusty rumor started
Logic follows that if a nail has been sitting outside long enough to get rusty, it's likely been exposed to soils containing the bacteria. Rust's rough texture on the surface of a nail also creates countless microscopic hiding places for bacteria.