They are the latest craze in running.
But a NewsChannel 5 investigation has discovered those popular color runs may not be as safe as you may think.
Color runs are usually a 5K and, as you run, volunteers throw colored powder at you. By the end of these events, participants are usually covered in it.
But our investigation has found that such fun runs could easily and quickly turn to tragedy.
Back in June, clouds of colored powder burst into flames at an event at a water park in Taiwan, creating a giant fireball. More than 500 people were hurt, many of them severely burned.
More than a dozen people died.
So could something like this happen at a color run?
We worked with the Naples, Florida fire department to test the same sort of colored powders for us to see if they would burn.
And did they!
"I think it's worse than even we could have imagined," said Fire Chief Stephen McInerny as he watched the experiment.
Just as volunteers spray powder over the runners who line up at the start of a race, firefighters sprayed it over a flare and got spectacular results.
The entire stream of flying powder ignited and became a stream of flaming color.
And just as volunteers toss handfuls of powder at runners at various spots during these races, in another test, firefighters tossed handfuls into the air over a flare and got instant flames.
Chief McInerny reacted, "It looks like burning gasoline."
Race organizers say the powder they use is a dyed cornstarch that is 100 percent safe.
But McInerny told us cornstarch is a carbohydrate and starch that readily burns.
"And when it's mixed or atomized in the air, it's explosive," he added.
In the Taiwan fire, there was a giant cloud of this powder shot out over the crowd right before the fire.
Investigators still have not figured out what set it off.
But you'll often find the same kind of clouds of powder over the crowds that gather at these color races.
"I think that was probably the most concerning that these events throw this powder in the air, they actually advertise and promote you throwing it above your heads all at once," Chief McInerny observed.
And that's exactly what happened several times both before and after a recent color run in Nashville.
When it did, the powder was so thick, you could barely see just feet in front of you.
"And if there's an ignition source, everyone's engulfed in flames at one time," the fire chief explained.
And McInerny isn't the only one who's concerned.
After the tragedy in Taiwan, government officials there immediately banned the use of these powders until they could determined if they are safe. In the U.S., the Kansas State Fire Marshal issued a warning about color runs, stating "most of these events generate sufficient colored powder and cloud dispersion...to create a fire hazard."
Back in Florida, after watching the fire test, the Naples fire marshal told us that, if it were up to him, color runs wouldn't be allowed.
"Under the right conditions, a very joyous event can turn into a real tragedy by having people getting horribly burned," Fire Marshal Robert Rogers said.
And, that's why people who do these color runs need to be warned.
"I think you have extreme danger. You're putting yourself in extreme danger," Chief McInerny said.
Fire experts say this powder is like paint and coal dust which is also highly combustible and under the right conditions, they say, a simple spark, electrical equipment, a hot surface, or static electricity could ignite it.
So what about breathing all that powder? Can that be good for you?
NewsChannel 5 Investigates had the colored powder analyzed. And we're just getting the preliminary results of the tests back now.
We'll have the results Tuesday on NewsChannel 5 at 6 p.m.
But, after you see what we found, it likely won't just be fire and flames that you'll be worried about at these runs.