The extract coming from Buchu, a South-African medicinal plant traditionally used to treat urinary tract infections.
As for skincare, the main active component of Buchu leaves is a flavonoid called diosmin that can act as an APN (aminopeptidase N) inhibitor. APN is an enzyme that plays some role in the sebocyte (the skin cells that create sebum) differentiation and sebum generation process and inhibiting it means less sebum produced by the skin.
The manufacturer did some in-vivo tests with 20 volunteers for 28 days and found that Barosma Betulina Leaf Extract does have a "statistically significant" sebum regulating effect, though do not expect miracles, the average reduction of sebum was only 13% that we think is not that much.
Show me some proof
- Kiss, A., A. Polcyn, and J. Kowalski. "Metallopeptidases ACE, NEP and APN inhibition by plant extracts." Acta Poloniae Pharmaceutica–Drug Research 62.4 (2005): 299-302.