Mustard oil is a hazardous oil because of its high content of allyl isothiocyanate.
The powder or seed does not contain allyl isothiocyanate as this is only formed during the production of the essential oil.
It is an annual plant with a much-branched stem, and lobed, roughly lyre-shaped leaves, 16cm (6 in) long. Bright yellow flowers are produced all summer, followed by small, erect, 4-angled pods with dark brown seeds.
In herbal medicine, the seeds are used to aid digestion, to promote the appetite, and for colds, chills, coughs, chilblains, rheumatism, arthritis, lumbago, and aches and pains.
As an essential oil, mustard oil is toxic because of its high content of allyl isothiocyanate. The oil is a skin and mucus membrane irritant.
Mustard oil is extracted from the black mustard seeds, which have been macerated in warm water by steam or water distillation.
Although mustard seeds and powder do not contain allyl isothiocyanate, it is formed when the seeds came in contact with water and the essential oil is formed when a glycoside decomposes due to enzymatic action.
The essential oil is not present in the fresh seeds or the powder, and so preparations made of these do not contain Allyl isothiocyanate.
White mustard seeds do not contain any essential oil.
The main chemical component of mustard oil is no less than 92% allyl isothiocyanate