The presence of animal dust correlates to a lower risk of developing asthma; tobacco smoke and moms with stress and depression are associated with a higher risk.

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Kids living in houses with cats, mice and cockroaches may have a lower risk of asthma, new research from Washington University shows.

The researchers looked at 442 kids living in the inner cities of St. Louis, Baltimore, Boston and New York City. They analyzed dust taken from the kids’ homes to measure the concentrations of cockroach, mouse and cat allergens. They found that higher levels of the allergens during infancy were associated with a lower risk of developing childhood asthma, a lung disease marked by inflammation in the airways.

The kids’ umbilical-cord blood was also analyzed, and researchers found that those who had been exposed to tobacco smoke in utero had a higher risk of asthma. Higher asthma rates were also related to moms who reported higher levels of stress and depression.

“This study suggests we may not be focusing on the right targets for preventing asthma in the inner city,” co-author Dr. Leonard Bacharier, a Washington University asthma specialist, said in a statement.

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“We may not need to worry about making sure the household environment is maximally clean — in fact, it’s possible that could be counterproductive. But helping women manage the challenges of mental health may make a difference.”

Since the study is based on observations, it cannot prove that any pet or pests can prevent or cause asthma. It merely suggests a potential link.

The research was published in the Journal of Allergy and Clinical Immunology. It was funded by the federal government and included researchers at Boston University, Columbia University, Johns Hopkins University, U.C. San Francisco and the University of Wisconsin-Madison.

The children in the study had at least one parent with asthma or allergies, so they were at higher risk of developing the disease.

Nearly one-third of the children were diagnosed with asthma by age 7. Cockroach allergens were found to be most protective against asthma, with mouse and cat allergens also showing a benefit.

While the research seems to contradict the idea that feces and saliva of cockroaches can trigger asthma, the key might be a bacteria attached to the allergens, Bacharier said.

The study also supports a shift in pediatric medicine toward early exposure to allergens such as peanuts in an effort to avoid allergies.

A pristine environment in infancy could cause the immune system to overreact later in life when the child is exposed to allergens, the theory goes.

Asthma researchers have long looked at animal exposures to find any hints at the development of the lung disease.

The research has often been conflicting. With so many genetic and environmental factors influencing asthma, it is very difficult to separate animal exposures to determine any link.

A 2015 study showed a relationship between early exposure to dogs and farm animals and a lower risk of childhood asthma. But dogs were named an asthma culprit in this 2010 report. Other research has shown higher rates of asthma among cat owners. And here’s one that shows cats reduce kids’ asthma risk.

The bottom line is the risk of asthma should not be a main factor in deciding whether or not to get a pet. And a little dust around the house may not be a bad thing.