Skin, it's what covers your bones and what you rub creams on to see how many blisters you can raise. If you don't rub poisons onto your skin to observe the after effects, you can thank one Dr. Kligman for doing the research for you.  Dr. Kligman discovered that prisoners have skin and that they were willing to sign up for experiments so he got them to sign a bunch of papers that they didn't understand and then he got busy.  For 20 years, starting in the 1950s and ending in 1973, Kligman injected the inmates of Holmesburg prison with poisons, had them rub cancer causing agents onto their skin, and charted the results.  He also sewed human organ tissues into their bodies to see what would happen - maybe the organs would regrow!  Maybe prison could become a farm for regeneration of human tissues and organs!

Dr. Kligman became a world famous dermatologist (there is one of a world famous anything and Kligman is it for skin doctors).  He discovered Retin-A (retinol) and every morning people across the world rub away their wrinkles and acne thanks to the work of Dr. Kligman - the hero of skin.

But the city of Philadelphia doesn't think he's such a hero and issued an apology in October of 2022 for giving sanction to the work of an unethical dermatologist.