DALLAS - "I don't think people need to panic, they just need to be aware," said Dr. Alfred Johnson, an Internal Medicine doctor from Richardson.
Dropping pesticide from the sky naturally raises questions -- ones that at least 20 patients are putting to Dr. Johnson.
"I tell them if they can, and they're real sensitive, to leave town," he added.
He doesn't suggest everyone needs to evacuate, but only certain people.
"People that already have lung disease, asthma, hypersensitivity, allergies - are more susceptible," Johnson said.
The chemical, called Duet, will rain down on Dallas County beginning at 10:00 p.m. Thursday.
The official Material Safety Data Sheet on Duet says it could cause a burning or prickling sensation to skin, tearing and blurred vision if exposed to someone's eyes, and respiratory irritation if inhaled.
Regardless, aerial spraying is a common way to fight the West Nile virus.
Health officials insist it effectively reduces the threat.
Houston has used aerial spraying every year for a decade, according to Dr. Rudy Bueno, Harris County Mosquito Control. He said contractors hired by the county even doused all of Harris County after Hurricane Ike in 2008.
"For a day or two, it would make sense not to wear your shoes that you wore outdoors [when you go] indoors and be careful about what you touch," Johnson said.
Still, it's hard to predict who or how many could have reactions to it.
Dr. Johnson said the spray should be settled by the time people get up to go to work Friday morning. But since the pesticide is oil-based, it will likely stay around longer than some others.