Animal toxicity studies indicate that Propyl Gallate was slightly toxic when ingested, but no systemic effects were noted with dermal application.

This is from the NIH's review of the preservative in the McRib to determine it's safety in cosmetics. The preservative is added to stablize and prevent rancidity of the fats used in cosmetics. So, a McRib is less dangerous if you use it as a moisturizer versus eating it.