After decades of perpetual increase, childhood asthma rates are finally going down in the United States. These results come from a thirteen year long study started in 2001 involving over 150,000 children. The study was lead by Dr. Lara Akinbami from the National Center for Health Statistics. The results were published in the journal of Pediatrics two weeks ago.

From 1980 to 1995, childhood asthma rates doubled in the US in part because of increasing awareness and diagnosis of the disease. The new study shows that rates continued to increase until they hit a peak at 9.3% in 2010. After that, the rate began to decrease and was at 8.3% when the study ended in 2013.

However, asthma rates vary across ages, races and regions. The most significant decline in asthma rates were seen in children below age 5, Mexican children, Midwestern children, and children from families that weren’t poor. Asthma rates stayed roughly the same in black children, and white children from the Northwest and West. Asthma rates increased in children aged 10 to 17, children from the South, and children from poor families.

It is unknown what factors have caused asthma to decline overall. One possibility is that air pollution in the United States has also declined over the last several years. Either way, the study is good news. Although, Dr. Akinbami warns, “We’re cautious because we never know what the next year is going to show.”