Black mustard is a plant. The seed and oil from the seed are used to make medicine. Black mustard oil is used for the common cold, painful joints and muscles (rheumatism), and arthritis. Black mustard seed is used for causing vomiting, relieving water retention (edema) by increasing urine production, and increasing appetite. Some people make a paste by mixing ground black mustard seed with warm water. They pack the paste in cloth and apply the cloth directly to the skin as a mustard plaster. This preparation is used for treating pneumonia, pain and swelling (inflammation) of the lining of the lungs (pleurisy), arthritis, lower back pain (lumbago), and aching feet. In foods, black mustard leaves (greens) are used in salads and other dishes. Also in foods, black mustard seed is used as a spice and to flavor mustard condiment. There are approximately 40 different species of mustard plant. Three different types are generally used to make the mustard condiment. Black mustard (Brassica nigra) is the most pungent. White mustard (Brassica alba) is the most mild and is used to make traditional American yellow mustard. Brown mustard (Brassica juncea) is dark yellow, has a pungent taste, and is used to make Dijon mustard. It is easier to harvest the brown mustard seed than the black mustard seed, so many mustard condiments now contain brown mustard seed instead of black mustard seed.