Among all the urban areas in Texas, Houston alone had an ozone warning today.
Ozone forms when the right weather patterns mix together the right ingredients from other pollutants.
Matt Tejada is with Air Alliance Houston.
"We load up our atmosphere with all the pollution from the cars and the refineries and everything else in the Houston area, and then it just sits there and cooks in some really nice weather."
Contrary to what many people think, it's not necessarily the blazing hot days of deep summer when this occurs most often, at least around here.
"And unfortunately for the Houston region, we will usually have those sorts of weather conditions on really nice days in late spring and early fall. Where we have some dry air, we have some bright sunshine, light breeze, those are perfect for ozone formation."
On top of that, it's also ragweed season.
Dr. David Corry conducts research on allergies at Baylor College of Medicine, and also treats patients at the VA hospital.
"It's more of a problem nowadays compared to earlier generations."
Ragweed pollen spreads far and wide, and is a huge allergic trigger for humans.
Plus, it seems the ragweed plant has flourished in recent decades.
"It's hard to be sure but it's just that we've so altered our environment particularly in rural settings with farming and agriculture and in other things that disrupt the environment, that leads to the massive overgrowth particularly of this weed."
On the other hand, recent decades have also brought medical relief too.
There are now non-drowsy forms of antihistamines, and nasal steroids like Flonase.