Answer:

allergen

Answer	Crossword Clue
ALLERGEN	It may cause a reaction
ALLERGEN	Sneeze cause
ALLERGEN	Tobacco smoke, perhaps

ALLERGEN	Bee venom is one
ALLERGEN	Pollen, perhaps
ALLERGEN	Reaction causer
ALLERGEN	Sneeze-causing substance
ALLERGEN	Pollen, e.g.
ALLERGEN	Dust, for one
ALLERGEN	It may lead to a breakout
ALLERGEN	Dust or pollen, e.g.

ALLERGEN	Pollen, often

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.