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Allergy to airborne pollen grains from certain grasses, weeds and trees is common in people with asthma and:
- May worsen asthma symptoms during the pollen seasons (usually in spring and early summer or during the dry season in tropical regions)
- Is usually caused by grasses, weeds and trees, which are wind pollinated
- Is not usually caused by Australian native plants (although there are exceptions, such as the Cypress Pine)
- Is not usually caused by highly flowered plants as they produce less pollen (which is transported by bees) than wind pollinated plants