Ever been outside during the warm months?
Lots and lots of tree hay, etc. pollen!
Trees could have occasional graphical effects of pollen falling from them during the right seasons.
Hearthlings should also be exposed to some allergic reaction during these seasons.
This wound could give debuff to FEP gain from foods, as you would have impaired taste.
Actual effect wouldn't have to be too severe, the main point being the added immersion, as you feel the seasons change and have all kinds of effects on your daily life.
Of course you would only get this wound when outside, so in caves/houses you'd not have to worry.
Could be just a few days out of spring or such when this happens.