Like coconut oil, mango butter extracted from the kernels of the mango tree (Mangifera indica) has been used in traditional medicine for centuries. There's a good reason why: Mango butter and oil are rich in fatty acids that make them excellent emollients.
The fats in mango butter are composed mostly of oleic and stearic acids. This makes mango butter a powerhouse at adding softness and moisture to the lips. These two acids are triglycerides, of which sebum is largely comprised. Adding it directly to your lips in the form of mango butter or oil is a natural, but artificial, way of restoring moisture to your lips.
Oleic and stearic acids also have the added benefit of being both hydrophobic and hydrophilic. One end is attracted to water, while the other end repels it, making these two triglycerides excellent at locking moisture in lips and waterproofing lips as well.