According to US Baby experts:

Most mosquito repellent incenses are made of refined pyrethrum and the released pollutants may cause strong toxic effect to human body even aggravate asthma, thus resulting in breath shortness. Even worse, the micro particles and gas will be drawn into the lungs and might cause cancer. In mosquito active summer days, US Baby experts recommend healthy and safe mosquito repellent methods to minimize potential harm to your baby.