Researchers at Stanford University looked at teens who were exposed to wildfire smoke this year in Fresno, Calif.
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The study found those teens had an increased amount of inflammatory markers in their blood.
That would make them more prone to getting asthma and developing genetic changes to their immune systems.
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"During a wildfire, we can't go by whether or not we smell it in the air. Even if we don't smell it, the particles can be inhaled and damage our health," said Mary Prunicki, M.D., PH.D of Stanford Medicine.
Yearly, about 7.6 million children and teens are exposed to wildfire smoke across the U.S.
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Researchers say no exposure is better and warn parents to keep children and teens inside while smoke is detected in the air.