3 ms·

I'm not sure why fats would be difficult to wash off, and soaps are made from fats through saponification.[1] [1] https://en.wikipedia.org/wiki/Saponification

• metalliqaz 4y ago
  Fats and oils are hydrophobic.
• v8xi 4y ago
  the process of saponification adds a hydrophilic/water-soluble end to a hydrophobic molecule (fat - which is essentially a long hydrocarbon chain). The fatty end embeds itself in fats/oils which then form what are called micelles with the fatty tail and dissolved greasy molecules on the inside and the water-soluble bit on the outside. Thus it essentially packages up all the grime in little balls that act as if they are dissolved in water and can thus be washed down the drain.