Mustard oil is traditionally used in North Indian cuisine and many Bengali fish dishes. Unfortunately, mustard oil also frequents news, where adulterated mustard oil causes dropsy in its consumers. What probably many Indians are unaware is that in the west, the sale of mustard oil for food is illegal (US, Canada and EU), largely because of two compounds found in the oil. One is an irritating compound called isothiocyanate and the other one an unusual fatty acid called 'erucic acid'. Mustard oil, contains copious amounts of Erucic acid (about 42%), which is known to cause heart damage in laboratory animals.
Many scientists believe that Erucic acid can cause accumulation of triglycerides in heart, fibrotic lesions in heart and lung cancer. Its effects though on humans are unknown, as it is not studied. Hence, just to be on the cautions side, its best to avoid mustard oil, especially when many other oil alternatives are available.