Sotolon (maple syrup, curry, fenugreek) Thiols Thioacetone (2-propanethione) A lightly studied organosulfur. Its smell is so potent it can be detected several hundred meters downwind mere seconds after a container is opened. Allyl thiol (2-propenethiol; allyl mercaptan; CH2=CHCH2SH) (garlic volatiles and garlic breath) (Methylthio)methanethiol (CH3SCH2SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice Ethanethiol, commonly called ethyl mercaptan (added to propane or other liquefied-petroleum gases used as fuel gases) 2-Methyl-2-propanethiol, commonly called tert-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas. Butane-1-thiol, commonly called butyl mercaptan, is a chemical intermediate. Grapefruit mercaptan (grapefruit) Methanethiol, commonly called methyl mercaptan (after eating Asparagus) Furan-2-ylmethanethiol, also called furfuryl mercaptan (roasted coffee) Benzyl mercaptan (leek or garlic-like) Miscellaneous compounds Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known) Phosphine (zinc phosphide poisoned bait) Diacetyl (butter flavor) Acetoin (butter flavor) Nerolin (orange flowers) Tetrahydrothiophene (added to natural gas) 2,4,6-Trichloroanisole (cork taint) Substituted pyrazines Aroma-compound receptors Animals that are capable of smell detect aroma compounds with their olfactory receptors. Olfactory receptors are cell-membrane receptors on the surface of sensory neurons in the olfactory system that detect airborne aroma compounds. Aroma compounds can then be identified by gas chromatography-olfactometry, which involves a human operator sniffing the GC effluent. In mammals, olfactory receptors are expressed on the surface of the olfactory epithelium in the nasal cavity. Safety and regulation In 2005–06, fragrance mix was the third-most-prevalent allergen in patch tests (11.5%). 'Fragrance' was voted Allergen of the Year in 2007 by the American Contact Dermatitis Society. A recent academic study in the United States has shown that "34.7 % of the population reported health problems, such as migraine headaches and respiratory difficulties, when exposed to fragranced products". The composition of fragrances is usually not disclosed in the label of the products, hiding the actual chemicals of the formula, which raises concerns among some consumers. In the United States, this is because the law regulating cosmetics protects trade secrets. In the United States, fragrances are regulated by the Food and Drug Administration if present in cosmetics or drugs, by the Consumer Products Safety Commission if present in consumer products. No pre-market approval is required, except for drugs. Fragrances are also generally regulated by the Toxic Substances Control Act of 1976 that "grandfathered" existing chemicals without further review or testing and put the