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.

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.

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. 

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