In recent weeks, tens of millions of Americans have lived and breathed through a thick haze of wildfire smoke. In places, it lasted for weeks. The immediate health effects of that are well known to the medical community and anyone who’s been exposed: Eyes sting, throats tighten, snot can turn black. Respiratory problems like asthma and chronic obstructive pulmonary disease (COPD) can be exacerbated, causing spikes in hospital visits. Much less is known though about what happens after the smoke clears.