Tragacanth gum is a natural binder, helping other ingredients to stick together. When in contact with water, it swells slightly and gets a mucilaginous texture that is soft and soothing to the skin.
Tragacanth is a group of plants of the genus Astragalus cultivated for their gum. Astragalus gummifer, the most commonly used species for this production, is native to Western Asia.
Gum is a type of resinous sap that flows from certain plants (usually of the Fabaceae family) when they're injured. It's a protective system, like a bandage, to prevent dehydration, infection and insects nibbles. They have been collected and used in cosmetics, incense and medicine for centuries, the most popular being the acacia gum.