粪臭素即3-甲基吲哚，为一种具有中等毒性的白色结晶有机化合物，是吲哚的一种衍生物。在自然界中，存在于哺乳动物的粪便（为色胺酸在消化系统中的产物）、甜菜与煤焦油中，具有强烈的粪便气味。在低浓度下，粪臭素具有花香味，并存在于许多花朵与精油中，如橙花、茉莉与Ziziphus mauritiana，因此被用于香水中的香精、定香剂以及食物香料等。其名称来自于希腊文的skato-，意指「动物的粪便」。

实验显示，粪臭素会造成山羊、绵羊、大鼠与某些品种小鼠的肺水肿。其似乎会选择性攻击Clara细胞，亦即肺中细胞色素P450酵素主要的集中处。这些酵素会将粪臭素转换为反应性中间体3-亚甲基假吲哚，此产物与蛋白质形成加合物而伤害细胞。

Skatole or 3-methylindole is a mildly toxic white crystalline organic compound belonging to the indole family. It occurs naturally in feces (it is produced from tryptophan in the mammalian digestive tract) and coal tar and has a strong fecal odor. In low concentrations, it has a flowery smell and is found in several flowers and essential oils, including those of orange blossoms, jasmine, and Ziziphus mauritiana. It is used as a fragrance and fixative in many perfumes and as an aroma compound. Its name is derived from the Greek root skato- meaning "dung". Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919). Skatole is also used by U.S. military in its non-lethal weaponry; specifically, malodorants.