Non-medical person here, but my question, I think, is on topic for this site.
Every time after I've gotten a vaccine injection I've always been given a variation of the same advice - "Don't wash/wet that place today/24h". I once ignored that just to see what happens, and the site got reddish, swelled a bit and became sensitive for a few days. Perhaps some sort of inflammation?
What I don't understand is - why? The puncture hole is tiny and closes almost instantaneously. There's no way any infection can get in through there, right? And if it was just about infection, I'd expect to see the same reaction any time I cut myself by accident. More so because those wounds usually close much slower. But that doesn't happen. What's going on here? Is this even true, or just a part of local medical tradition?
I've tried searching for this on the internet but I cannot find anything.