Erucic acid is a monounsaturated omega-9 fatty acid, denoted 22:1 ω-9. It is prevalent in rapeseed, wallflower seed, and mustard seed, making up 40 to 50 percent of their oils. Erucic acid is also known as cis-13-docosenoic acid and the trans isomer is known as brassidic acid.
Erucic acid is used to produce emollients, surfactants, and other chemicals. Erucic has been shown to have a variety of health impacts in studies, and foods containing large amounts of erucic acid are considered unfit for human consumption in many countries. Canola is a special variety of rapeseed oil that contains less than 1% of the unwanted erucic acid. A four-to-one mixture of erucic acid and oleic acid constitutes Lorenzo's oil, a potential treatment for the rare neurobiological disorder adrenoleukodistrophy (ALD).