Hydroxypinacolone Retinoate is also known as HPR. It is a retinoic acid ester and is said to be gentler on skin than using retinol. Currently, you can find it in Sunday Riley’s Luna Oil, Philosophy’s Miracle Worker and Dermalogica’s AGE smart line. Hydroxypinacolone Retinoate has promise but there isn’t a compelling amount of data evaluating its effectiveness, or comparing it to other forms of retinol (like retinol or retinaldehyde). The one study that does exist on this ingredient was conducted by the brand that manufactures hydroxypinacolone retinoate, and was conducted on just five people (GrantIndustries.com, 2015).