Allergies and airborne irritants are often cyclical, depending on the season. Recent studies have suggested that global climate change may be affecting the length of so-called allergy season, as well as the severity of air allergies.

The U.S. Department of Agriculture (USDA) recently released a report stating that higher levels of carbon dioxide have opened the door to an increase in the production of ragweed. This pathogen’s presence appears to be boosting the severity of air allergies in the U.S.

The USDA estimated that in 40 or 50 years, the amount of ragweed pollen in the air has doubled. In laboratory tests, scientists found that doubling the amount of carbon dioxide in the air may quadruple the level of pollen given off by ragweed plants.

The agency also noted that while less ragweed grows in urban areas, those with allergies often have increased sensitivity to its pollen due to air pollution.

More than 36 million Americans suffer from ragweed allergies, according to the American Academy of Allergy Asthma and Immunology. The Academy notes that those with this sensitivity may notice symptoms when consuming bananas, cucumbers, zucchinis and melons.

To ensure adequate vitamin levels, those with air allergies may consider taking daily .