system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - How do ointments used to treat body parts besides the skin (like ointments for muscle pain or joint pain) work? Do they even work?
gpt
Really depends on the ointment. 

Some have lidocaine or related meds that work as direct numbing agents- think novacaine. It can block the nerves from the whole region, even beyond the skin. 

Others have drugs like aspirin, which absorb through the skin and act as they would if they were swallowed

Still others have capsaicin, which gives the sensation of heat. It makes the body respond as if it was actually hot, relaxing the muscles. Or menthol, which acts as a cooling and numbing agent.