Foul-smelling gas usually has a simple cause, such as eating high-fiber foods or certain medications. However, it can also be an indicator of a health condition. Common causes of smelly farts include eating foods with high sulphur content, such as cruciferous vegetables, beans, and dairy products, as well as being lactose intolerant, having a bowel obstruction, or having inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis. If your farts smell especially bad, it is recommended to speak to your doctor to rule out any underlying health conditions.