IDK... maybe pine allergies run in my family, but I definitely have welts from handling pine (other than the bark), so I wasn't shocked when it triggered by the pollen, too. I am also allergic to grass pollen (but not touch) to a lesser extent. DS is allergic to touching grass (welts on his skin when younger, IDK if it still happens, we don't sit on grass in the summer, you know?)
I have heard the same thing about cottonwood pollen size... and yet, the allergies for some people are only when cottonwood is blowing, and are worse next to the heaviest cottonwood tree areas, rather than near a mixed grove or open area... you start to notice these things closely when they cause emergency room visits due to acuteness and severity.