According to multiple studies, mosquitoes have a preference for certain blood types. Research studies indicate that mosquitoes prefer people with type O blood over other blood types. A 2019 study found that the major mosquito vector of dengue virus also preferred people with type O blood to those with other blood types. However, separate research notes that the science is contradictory and that blood type is not the only factor that influences how much mosquitoes like you. Mosquitoes detect blood types through chemical signals secreted through human (and animal) skin, and people secrete certain chemicals through their skin that attract mosquitoes, such as lactic acid. Other factors that attract mosquitoes include carbon dioxide, heat, and chemicals found in sweat.