Pennsylvania Allergy Season Guide

Pennsylvania experiences a humid continental climate with four distinct seasons — cold, snowy winters and warm, humid summers.

Birch, oak, maple, and beech produce an intense April-May tree season. Grass pollen peaks in June, and ragweed lasts from mid-August through October.

Humid summers, dense tree cover, and heavy leaf decay drive elevated Alternaria and Cladosporium counts from late summer into fall.

Allergy patterns vary by elevation and proximity to coast or mountains within Pennsylvania, but most of the state shares a common seasonal rhythm of spring tree pollen, summer grass pollen, and late-summer to fall weed pollen.