What is "allergens"

Usage examples of "allergens".

Better than the sweet air of Pennsylvania, and all the hidden allergens and catalysts it might be carrying.

It was all she could manage with her lungs burning from exertion and skunk gas and her elbows and knees itching as badly as her ears from the irritant darts, but she knew better than to scratch at them because that only spread the allergens, and meanwhile she had to bite her lip hard and dig her nails into her palms to stop herself from scratching.