Guaiacol is a naturally occurring compound present in wood smoke, resulting from the pyrolysis of lignin. The compound contributes to the robust flavor of roasted coffee and whiskey.

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Guaiacol is a phenolic product first isolated from Guaiac resin, a substance produced from the tree species Guaiacum, and the oxidation of lignin. It is an aromatic oil with a yellow tint that is now commonly derived from wood creosote or Guaiacum.

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Guaiacol is a precursor to a variety of food flavors, such as eugenol (found in clove oil, nutmeg, cinnamon, basil, and bay leaf) and vanillin. Over 80% of the global supply of vanillin is estimated to come from guaiacol.

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Medicinally, guaiacol is used as an expectorant, antiseptic, local anesthetic, and is even used in traditional dental pulp sedation.

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Guaiacol is an oily yellow liquid with a penetrating odor obtained by distilling wood tar or creosote. It is also present in wood smoke, resulting from the pyrolysis of lignin. The compound contributes to the flavor of many substances, such as whisky and roasted coffee.