Pollen allergies will become even more common than today over the next 100 years, researchers warn. Grass pollen and allergen exposure could increase by up to 202 percent over the course of the coming century.

University of Massachusetts Amherst researchers believe increases in the concentrations of carbon dioxide and ground-level ozone could lead to more extreme conditions for allergy sufferers. Greater concentrations of carbon dioxide in air can assist in the growth of plants, including those that are responsible for allergy symptoms in humans.

Grasses were examined in four enclosed tanks, allowing researchers to carefully control the atmosphere within each environment. In one tank, levels of carbon dioxide were raised to twice the levels measured today, while ozone concentrations were kept the same. In a second habitat, levels of ozone were more than doubled, from 30 to 80 parts per billion. Both gases were raised in the third environment, while the fourth served as a control, with a contemporary atmosphere.

"The implications of increasing CO2 for human health are clear. Stimulation of grass pollen production by elevated CO2 will increase airborne concentrations and increase exposure and suffering in grass pollen-allergic individuals," Christine Rogers from the UMass Amherst School of Public Health and Health Sciences (SPHHS) and other researchers stated.

Increased carbon dioxide levels were shown to raise the production of pollen by 53 percent, as noted by measurements of the allergen protein Phl p 5.

Ozone did not appear to alter the production of pollen in the plants examined, although it normally tends to stunt plant growth. However, the gas is known to affect the mucous membranes in humans, making allergy symptoms worse for many people.

Allergies to grass pollen can cause headaches, wheezing, and difficulty breathing, experienced by roughly 20 percent of Americans. In extreme cases, sufferers can even be forced into emergency rooms with severe symptoms.

"While it is expected that people with pre-existing allergies will have more pronounced symptoms in the future, we don't yet know whether this dramatic increase in pollen will also cause more people to develop allergies," Rogers told the press.

Levels of carbon dioxide seen in the study were around 800 parts per million (ppm), and many researchers believe extreme environmental damage could occur if levels reach just 450 ppm, up from today's concentrations of 400 ppm. International agreements could soon limit emissions of greenhouse gases to levels far below that examined in the study.

Study of the role carbon dioxide and ozone levels play in allergies was detailed in the online journal PLOS One.