system
Given the following post, respond as if you're commenting on Reddit:
human
Why does normal pain medicine helps you with a headache for a few hours but not make you immune to all pain?

I know basic pain medicaments block some kind of chemical reaction in you body for a while, and this reaction is the base of your pain (extremely simply). But why when I use pills for headaches I still can feel pain from hitting my little toe on a bed?
gpt
There is a difference between pain, inflammation, and sensitivity after an injury. Not all injuries feel the same, but they all go through these stages at different rates. After an injury you'll feel pain which includes inflammation, and as the inflammation subsides and new tissue is being formed in place of place of dead tissue, sensitivity.

The most common pain medications that you don't need a prescription for are anti-inflammatories. These are really good for swelling and pain caused by immune system responses. It's basically  slowing down the increased blood flow that causes the redness, swelling, and hot feeling you get after an injury or infection.

Headaches are mainly caused by increased pressure inside the skull. the vessels in the brain increasing in size, usually due to inflammation or higher blood pressure. Anti-inflammatories reduce the swelling happening in your brain and relax and soothe vessels.

There is an enzyme that causes the release of prostaglandins , which increases blood flow to affected areas when they're injured , also known as perfusion. It's like calling an emergency services crew with mutual aid and special contractors to repair a busted dam or put out a massive fire. But  the body isn't good a regulating inflammatory resposes, which is why inflammation often causes more damage to surrounding tissue. Think of how you feel during a fever, that's mainly the side effects of your immune system.

The pain you feel from trauma isn't just inflammation, but direct injury and stimulation of afferent nerve fibers. opioids and other analgesics work in different ways to affect the nervous system to either slow or block pain signals.

Some medications like lidocaine block nerve signals in the area where it's applied. It's a sodium channel blocker that also blocks the neurotransmitter acetylcholine, which is used by nerves to send pain signals to the brain.