What is envelope glue made of?

Most envelope glue is made from gum arabic, which is the hardened sap of the Acacia senegal tree. Some envelope glue also contains petroleum. According to New York City dentist Thomas P. Connelly, envelope glue is safe to ingest.

Postage stamps and envelopes use the same type of gum arabic-based adhesive glue, but gum arabic has dozens of other uses. It is used to make marshamallows and candy, like M&Ms and jelly beans, soda, like Orange Crush and Mountain Dew, vitamins and cosmetics. Instant drinks, dessert mixes and soup bases use gum arabic to help prolong shelf life. It is also used to make crayons, laundry detergent, baking mixtures and aspirin.