As fire crews and air tankers work to block the wildfires' explosive growth, images of red clouds of fire retardant falling onto trees are common. What is it — and what's in it?

Crews battling the deadly ongoing Los Angeles wildfires have started dropping bright pink fire retardant known as Phos-Chek from the skies to combat the stubborn flames. The eye-catching flame retardant — seen in photographs coating homes,