In a study by the Journal of Medical Entomology, mosquitoes landed on people with blood Type O nearly twice as frequently as those with Type A. The researchers believe this may be due to secretions we produce, which tips mosquitoes off on a person's blood type. University of Florida entomology professor Jonathan F. Day also noted that mosquitoes pick up on cues we give off, such as the amount of CO2 produced, which increases the attractiveness of mosquitoes. Avoid peak activity times for mosquitoes, as sunrise and sunset are when they are active. DEET is a common ingredient in insect repellents and sprays with DEET are recommended if you know you're at risk of bites. Despite controversy over the health effects of DEET, a 2014 review by the Environmental Protection Agency found it does not pose a risk to one’s health, including children, pregnant women and breastfeeding women.