Nothing profound in this one, not even a pretty picture.
One difference between the UK and the land of the free is the use of body wash instead of soap. It’s actually a European trend that has gradually spread west. Darn EU. Body wash is sort of like shampoo, but uses coarser detergents (typically Sodium Lauryl Sulfate or Sodium Dodecyl Sulfate) and has fewer conditioners and scents.
In the UK I’m partial to the cheapest Tesco value product (blue coloured and 50p a bottle). A bottle lasts my boys and me almost two weeks, which is pretty good value (my wife still prefers soap). This time, after returning to the USA, I tried to find a similar product. Ivory makes one that’s 97 cents at Walmart.
You may ask “So what?”
It turns out the detergents are excellent at lifting soap scum. Soaps are sodium and potassium salts of organic acids – for example Sodium Laurate. As such they form coordination complexes with ions in the water, especially calcium, which precipitate into a hard, insoluble and scummy substance. It’s a real nuisance. The sulfate-based detergents don’t do this, and even better solubilize the scum.