system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How/why does skin moisturiser work?
gpt
A moisturizer as a product is like a soup made of different ingredients.

Some attract and retain moisture, like tiny sponges.

Some act as a barrier to not let water pass (as much), like putting hand in a plastic bag.

Some allow mixing both oil and water together.

Some fill tiny crevices in the skin, making it feel smoother.

Some make skin a little bit puffy which makes it look smoother.

Some reduce skin's reaction to things (which can be getting red or flaky).

Some help the outer (dead) skin layers to detach faster, making skin smoother.

Some change consistency, pH, smell, color.

Some prevent bad things to grow in it, like bacteria.

The goal of the final recipe is to create something that will make money, so as such, this takes priority over being useful or even being harmless.

In practice this could mean for example using too small amounts of useful stuff if they have some less sellable points (like glycerine being very sticky).

Or stuff that is in such tiny amounts that it is likely useless but sounds good on the label (like "silk protein" or "[something exotic] extract").

Or stuff that isn't very compatible, but won't be noticed by consumer. Like stuff that shouldn't be combined because of conflicting pH.

Or stuff that is potentially harmful or under-researched. Or has some benefits at a cost of some issues.