system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a specific reason why many people's arms tend to hurt after receiving a flu shot but not after many other shots?
gpt
There is a substance called Adjuvant that is an irritant included with some shots. Adjuvant stimulates your innate/non-specific/general immune response, by stimulating your innate immune response at the same time as the vaccine stimulates your specific/late/anti-body/adaptive immune response the adaptive immunity developed is stronger.