Rust is the result of the oxidation of iron in the presence of oxygen and moisture. This is a chemical reaction that can be represented by the equation:

4Fe + 3O2 + 6H2O -> 4Fe(OH)3xH2O

In the above equation, iron atoms react with oxygen and water molecules to form iron hydroxide, a reddish-brown compound that we commonly know as rust. This process is accelerated in the presence of salt or other corrosive substances, which explains why cars are more prone to rusting near the coast.