Risks and warnings
Pure, unregulated mustard oil can be pretty dangerous stuff. For example, one study found that mixing unadulterated mustard oil with argemone oil, a combination sometimes found in Indian food, can destroy red blood cells in the body. Any mustard oil that is contaminated with argemone oil is considered dangerous to humans.
When using mustard essential oil, you’ll also want to watch for allergies. Test a small amount of the essential oil on the skin away from your face or lungs. Wait 24 hours to see if you have a reaction before applying a larger amount. As with any essential oils, you should not use mustard essential oil on infants.