In 1567, Swiss physician Paracelsus suggested that an unidentified substance in mined ore (identified as radon gas in modern times) caused a wasting disease in miners, and in England, in 1761, John Hill made the first direct link of cancer to chemical substances by noting that excessive use of snuff may cause nasal cancer. Tumors were described more than 2,000 years before the discovery of chromosomes and DNA in 500 B.C., the Greek physician Hippocrates named tumors resembling a crab karkinos (from which the word "cancer" is derived via Latin), meaning crab. The first mutagens to be identified were carcinogens, substances that were shown to be linked to cancer. Not all mutations are caused by mutagens: so-called "spontaneous mutations" occur due to spontaneous hydrolysis, errors in DNA replication, repair and recombination. The process of DNA becoming modified is called mutagenesis. All mutagens have characteristic mutational signatures with some chemicals becoming mutagenic through cellular processes. As many mutations can cause cancer in animals, such mutagens can therefore be carcinogens, although not all necessarily are. In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. The international pictogram for chemicals that are sensitising, mutagenic, carcinogenic or toxic to reproduction ( April 2023) ( Learn how and when to remove this template message) Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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