For years now I have developed a headache following day hike hike. (not into backpacking much yet...am day hiking the AT right now - will prob never "finish" but that's not the point! ) I have thought these headaches were caused by dehydration and not eating enough so have been eating tons while I hike and making sure I drink lots and lots of water and gatorade. However I still get a headache after I hike. Well today I think I found the culprit - allergies. I have been fighting my 1st ever sinus infection which was still causing me pain after the infection was gone and I went to the dr and she told me to take Claritin and a Sudafed in the morning and that has helped...but after my hike today the pain returned and since it was so close to the sinus infection I remember exactly what that kind of headache feels like and this is it. It makes sense as when I was a kid I was told that I was allergic to everything outdoors and I disregarded that information because I didn't like it and I didn't get immediatly miserable like I did from horses and cats so I figured the dr was nuts. Also makes sense because I didn't get 1 headache after 5 days of hiking in Glacier NP in Montana - they don't have the same decidous trees there that we do here... So I'm wondering, does anyone else get allergy headaches after hiking? If so, what do you do about it?