A cosmetic factory or rejuvenation clinic was a place in which people would undergo heavy body alteration to remain youthful as they aged.
On the way to Hilldale, Foley had believed Jennifer Parker to have spent a bundle at a cosmetic factory as her appearance did not match her age. It also allowed Foley to start wondering about her story and how she ended up in a place like Hilldale, but knew that Reese would say it was just conjecture which had no place in police procedure.
Doc Brown got an "all natural overhall" to add 30-40 years to his life sometime between his first trip to the future and when he decided to bring Marty to the future to "do something about his kids". Treatments included hair repair, changing his blood and replacing his spleen and colon. However, he thought he looked so youthful that he then added prosthetic makeup so that Marty would recognize him.