Updated: May 22
In some cases, yes, but it doesn't affect all. There are many other things that can actually affect eczema in terms of dust, allergies, and even toxins in the air, which can be very irritable. Hot weather can cause sweating, stinging, and itchiness. Ultimately it comes down to diet and lifestyle issues in terms of what you're eating and what you're applying to your body. So it's not just down to one particular thing, but pollen can certainly be a trigger.
However, it doesn't apply to all and there are many contributing factors.