system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does bar soap seem to dry out my skin, but liquid soap doesn't?

I've recently started using bar soap again for the first time in like a decade, and noticed that even while in the shower, it seems to leave a "film" or just a sense of dryness on my skin. But I've never noticed this with liquid soap, or body wash. What is causing this? Are the two types of soaps significantly different?
gpt
Liquid soap isn’t “soap” technically, but actually synthetic detergents dissolved in water.  These were invented in the 1950’s when oil was scarce for making soap.  While soap and detergent are both technically surfactants, in that they are hydro and lypo philic, soap is usually very alkaline, more so than detergent, and your skin has a slightly acidic oil barrier.  When alkaline soap interacts with your acidic oil barrier, it’s very good at breaking it down, removing your skin’s ability to keep water in making it feel dry.  Liquid soap most definitely can dry out your skin, but most liquid soap has added humectants like glycerin that help to preserve the acid barrier during cleansing.