What is the worst spring allergen almost everywhere?

Tree pollen is the worst spring allergen almost everywhere, but the specific tree depends on your region—oak, birch, maple, or cedar. Check your local pollen forecast on weather apps or Pollen.com. Start taking a non-drowsy antihistamine before symptoms hit, usually mid-February or early March, and add a nasal steroid spray if needed. Shower after being outside, keep windows closed, and use an air purifier.