Your skin’s job is to play defense
Our skin’s main job is to act like a barrier. Most of the time, that’s a really good thing. If our skin let things in easily, we wouldn’t even be able to take a shower without turning into a puddle and we would be a lot more susceptible to toxins or infections.
In medicine and beauty, skin’s efficacy as a barrier is double-edged sword though: the thing that makes the skin such a good gate keeper is the same thing that also makes most skin care relatively ineffective.
Most creams, serums and lotions are wiped or sweated away before they can ever absorb. Even worse, many large molecules in popular formulations have no way of getting into your skin; only really small molecules can actually get through the skin without a needle. To put this into context, collagen is actually 300 times larger than what can actually be absorbed by your skin via a topical.