system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the difference between antihistamines and decongestants?
gpt
People sometimes (inaccurately) use them interchangeably but antihistamines are specifically for allergies. Histamines are compounds related to immune system response, and allergies are caused by hypersensitivity of the immune system.

Decongestants are just drugs that treat nasal congestion in the upper respiratory tract, which might be caused by allergies but could be lots of other things too.

If you just look at the labels on the drugs, you'll see the active ingredients are different. Some products might be a combination of the two, but it's just two different drugs mixed together.