It may cause a reaction

Usage examples of allergen.

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.

Bafforr tree pollen shows promise as an allergen that affects the armor, but it will be some time before the pollen can be synthesized in the amounts needed to serve as an effective deterrent or biological agent.

Meterios has become infected by whatever allergen Brad Karpla brought back from his latest hunt.

That is a rare but proven phenomenon—the proteids of one human body acting as allergens to another.