eli5: you know that film saliva leaves on the edges of cups or in your dog’s food bowl? What’s the purpose of it being kind of water-repellent and hard to remove even with soap?

Question

eli5: you know that film saliva leaves on the edges of cups or in your dog’s food bowl? What’s the purpose of it being kind of water-repellent and hard to remove even with soap?

In: 0

Answer 1

No, not biofilm—that’s from leaving water stagnant too long. I change my dog’s bowls every day and my coffee mug that I drink out of and both get it.

Answer 2

It’s skin oil (sebum), and its purpose is keeping the skin soft and to protect it. If it wasn’t resistant to water, our skin would dry out easily. And most soaps, including those for hand-washing dishes, are formulated specifically to be kind to our skin by not removing the oil.