Sodium Cocoyl Isethionate
Also known as "baby foam", sodium cocoyl isethionate is a very mild anionic surfactant which creates a beautiful foam with lasting, small bubbles.
It's derived from coconut oil but due to the way it's made, calling it 100% natural is maybe a bit of a long shot. However, it's a very nice, biodegradable surfactant which is great for use in facial cleansers, makeup removers, and shampoos. Too bad it's fairly expensive, so that not many brands use it!