system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do localised analgesics work?

Because I have nothing better to do, I often sit and think about random stuff.  
Tonight it's localised analgesics, injected or topical.  


I assume it's something to do with chemicals interacting with something and blocking signals, but I'm curious as to how it actually works.  
Thankings!
gpt
There aren't really localized analgesics. Analgesia means something that takes away pain. Many of the drugs that are used to treat pain can come in a form that is applied to the skin. For example, Aspercreme is aspirin, or opiods like fentanyl can be applied as a patch. However, these are not localized. They are absorbed through the skin and then into the blood, and can work all over your body just the same as if you took a pill. You are probably thinking of local anesthetics like lidocaine or benzocaine. Local anesthetics block nerve signals in general, including pain. If they are placed topically on the skin or injected just underneath it, it blocks the nerves right in that area and causes it to be numb. If they are injected around a major nerve, they can numb a much larger area, say your entire lower jaw or part of your leg, etc.