Shampoo doesnโt have to foam, but we add foaming chemicals because people expect it each time they wash their hair. Same thing with laundry detergent. And toothpasteโnow every company adds sodium laureth sulfate to make toothpaste foam more. Thereโs no cleaning benefit, but people feel better when thereโs a bunch of suds around their mouth. Once the customer starts expecting that foam, the habit starts growing.
Charles Duhigg