Butanethiol, also known as butyl mercaptan, is a highly volatile, clear to yellowish liquid with a foetid (extremely foul-smelling) odor, commonly described as "skunk" odor. In fact, butanethiol is one of the major constituents of a skunk's defensive spray. The scent of butanethiol is so strong that the human nose can easily detect it in the air at concentrations as low as 10 parts per billion. Butanethiol is chemically classified among the thiols, which are organic compounds with molecular formulas and structural formulas similar to alcohols, except that sulfur-containing sulfhydryl group (-SH) replaces the oxygen-containing hydroxyl group in the molecule. Butanethiol's basic molecular formula is C₄H₉SH, and its structural formula is similar to that of the alcohol butanol. Butanethiol is a thiol of low molecular weight, and it is highly flammable. Butanethiol is used as an industrial solvent, as an odorant for natural gas (which is odorless), and as an intermediate for insecticides and herbicides. It is sometimes placed in the "stink bombs" and "stink perfumes" that pranksters love to use.

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Butanethiol is a very noxious and caustic chemical compound, and at sufficiently high concentrations, it produces serious health effects in both humans and animals, especially as a result of prolonged exposure. Sufficiently high concentrations of the foetid, volatile substance causes eye irritation, headaches, nausea and vomiting, dizziness, and irritation of the respiratory tract. Even higher concentrations can lead to unconsciousness and coma after prolonged exposure. Contact with the skin and mucous membranes causes burns, and contact with the eyes can lead to blurred vision or complete blindness.