An analysis shows that their immune systems were lower than normal, 12 years after they were naturally exposed to wildfire smoke.
There are also indications that the animals passed on the defect to their offspring.
The findings have prompted an investigation into the impact of wildfires on the health of children.
The results were presented at the American Association for the Advancement of Science meeting in Seattle by Prof Lisa Miller from the University of California, Davis.
They are particularly pertinent given the recent spate of wildfires in Australia, California and Brazil.
Such fires are likely to become more common as a result of the drier conditions in many parts of the world, predicted by climate change models.
Prof Miller told BBC News that she now has enough evidence from her analysis of monkeys to look into how recent wildfires may have affected the health of children in Northern California.
“I believe very strongly that we now have enough evidence to move to the clinic. My plan is to look at records from paediatric populations and find evidence of increased asthma, increased respiratory, viral and bacterial infections, increased use of antibiotics and longer recovery times from illness.”
Prof Miller’s analysis is based on a study of rhesus monkeys kept at UC Davis’s outdoor National Primate Centre.
In 2008 the 4,000 or so animals located there were exposed to smoke from a wildfire in Trinity and Humbolt Counties, 200 miles north of Davis – as was the city’s human population.