Alpha hydroxy acid (AHA), also known as amygdalic acid. There’s scant research showing this to be an effective alternative to other AHAs, although it does have germicidal activity. Unlike glycolic acid, mandelic acid is light-sensitive and must be packaged in an opaque container to remain effective. 
- Ash M. Handbook of Cosmetic and Personal Care Additives. Synapse Information Resources, Inc.; 2002.