What is the principle of mosquito coils? Is it harmful to human body?

Mosquito incense is the use of high temperature combustion effect, the insecticide slowly released into the air, mosquito repellent effect is greater than the effect of killing mosquitoes.　As long as the electric mosquito incense five minutes, mosquitoes began to sleep, powerless to bite. Used indoors, there is no need, not suitable for the whole night open, and people and pets are best not to stay in the use of mosquito coils indoor, after thirty minutes of ignition, turn off the mosquito coils, and then enter the room; at this time, mosquitoes have been knocked unconscious, even if the mosquitoes awakened in the middle of the night, there is no strength to bite people again. If the burning will smoke mosquito coil, more inappropriate in the confined space all night pointing, as with electric mosquito coils, point thirty minutes can be.