Why do soap bars stop making foam/lather after they’ve been used for a while?

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Why do soap bars stop making foam/lather after they’ve been used for a while?

In: Chemistry
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In the manufacturing of soap, they actually add a lathering agent to make it foam up. Look up a surfactant for more info here. I believe Sodium laureth sulfate is a common surfactant used in soaps.
The pure ‘soap’ actually wouldn’t lather without this.

Anyway, soap manufacturers actually layer their soap bars. So the outside ‘layers’ contain this expensive surfactant, and the inner layers do not.
It’s done as a cost saving measure. The idea is that your opinion of the quality of the soap is heavily influenced by the first few uses.

I should add that the lathering itself has literally no effect on the effectiveness of the soap, but there is a perception that lathering is necessary.