A mutagen is a chemical or physical substance that corrupts genetic material, such as DNA or RNA. Mutagens create genetic mutations and increase an organism's risk for cancers and cell death. The two main types of mutagens are physical and chemical. A physical mutagen is in the form of a physical substance. The main physical mutagen is short wave rays which penetrate living cells and alter genetic material. Examples of this type of mutagen include ultraviolet rays and X-rays. A chemical mutagen is a mutating agent in the form of a chemical substance. These substances work by mimicking nitrogenous bases in genetic material that cannot be duplicated during DNA replication. Examples of this type of mutagen would be nitric acid or peroxide.