Shampoo has come a long way since it was first introduced in the 19th century. I remember when some shampoo company started advertising the idea that you should shampoo every day. That was a really novel idea at the time, since showers weren’t all that common in houses yet, and a lot of folks still didn’t have indoor plumbing. Craig Benzine guest-hosts this week’s mental_floss List Show, posted a little earlier than usual. He’s got facts about shampoo, including the reason there’s silicone in your shampoo.