Asthma triggered by a dust mite allergy can damage the DNA in lung cells. The ability of cells to repair this damage may determine the disease’s severity.

For many people, allergens such as dust mites, pet dander, and pollens are only a minor issue, causing a runny nose, itchy eyes, and sneezing.

But for people with asthma these allergens can cause the immune system to overreact — leading to coughing, wheezing, or difficulty breathing.

As severe as the outward symptoms of asthma can be, they only touch the surface of this condition, which affects millions of people worldwide.

Inside the lungs you’ll see inflammation and constriction of the smooth muscle that leads to the characteristic narrowing of the airways that is associated with asthma.

But according to a new study, you’ll find that damage occurs all the way down to the genetic level.

“DNA damage is a component in asthma development, potentially contributing to the worsening of asthma,” Bevin Engelward, Sc.D., a professor of biological engineering at MIT and a senior author of the study, said in a press release.

DNA damage is not, however, a one-way street. Cells do have the ability to fix what’s broken — a capacity that varies from person to person.

This ability, say researchers, may influence the severity of an asthma attack.

“In addition to activation of immune responses, patients’ DNA repair capacity may affect disease progression,” said Engelward.

The results of the study were published May 1 in the Journal of Allergy and Clinical Immunology.

Read More: What Causes Asthma? »

This is not the first study to show that asthma can harm a person’s DNA.

Last year, Robert Schiestl, Ph.D., a professor of pathology, environmental health, and radiation oncology at the UCLA Schools of Medicine and Public Health, and his colleagues found signs of genetic damage in the blood of people with asthma.

Doctors previously thought this kind of genetic damage was limited to the lungs.

The new study builds on this research to provide a better understanding of the mechanisms involved in a worsening asthma attack.

The researchers focused on the dust mite allergen because up to 85 percent of people with asthma are allergic to it.

In one experiment, Engelward and colleagues exposed the lungs of mice to proteins taken from dust mites in order to trigger an asthma-like condition. This resulted in several changes in the lungs.

“[Engelward] shows that house dust mite dust exposure causes inflammation, reactive oxygen species, DNA double-strand breaks, damage to proteins, and apoptosis,” Schiestl said in an email to Healthline.

Read More: Thirdhand Smoke Causes DNA Damage »

When a person with asthma inhales an allergen they are sensitive to, the immune system goes into overdrive.

Immune cells flood the chest and release molecules known as cytokines that cause inflammation and constriction of the smooth muscle in the lungs.

Exposure of the lungs to dust mite proteins can also stimulate the release of free radicals in the lungs — known as reactive oxygen and nitrogen species (RONS).

These free radicals can damage DNA, lipids, and proteins. They can also worsen an asthma attack.

Cells have built-in mechanisms for repairing damaged DNA, including a double-strand break that involves both strands of DNA.

If the repairs don’t happen, cells can die — a process known as apoptosis.

Read More: Can Mindfulness Meditation Reduce an Asthma Attack? »

The researchers saw similar changes in lung tissue samples taken from people with asthma.

“[Engleward] also found that lung cells from asthma patients had increased levels of DNA repair enzymes, cytokines, and double-strand breaks,” said Schiestl. “It is a nice confirmation of my previous work.”

Other research has shown that immune cells, such as eosinophils and neutrophils, release RONS.

In the new study, though, when researchers exposed lung tissue cells directly to dust mite proteins, they still found signs of free radical damage without immune cells being present.

According to the researchers, this suggests that the lung epithelial cells may release free radicals on their own when exposed directly to dust mite proteins.

In addition, when researchers used a drug to block the lung cells in mice from repairing the DNA, the researchers saw an increase in the amount of DNA damage and cell death.

More studies are needed to understand exactly what this means for the severity of an asthma attack in people.

But the researchers suggest that knowing how each person’s body responds to inflammation could one day help identify people at risk of more dangerous asthma attacks.

“Ultimately, screening for DNA repair capacity might be used to predict the development of severe asthma,” said Engelward.