You come in from a summer hike covered with itchy red mosquito bites, only to have your friends innocently proclaim that they don’t have any. Or you wake up from a night of camping to find your ankles and wrists aflame with bites, while your tentmates are unscathed.

You’re not alone. An estimated 20 percent of people, it turns out, are especially delicious for mosquitoes, and get bit more often on a consistent basis. And while scientists don’t yet have a cure for the ailment, other than preventing bites with insect repellent (which, we’ve recently discovered, some mosquitoes can become immune to over time), they do have a number of ideas regarding why some of us are more prone to bites than others. Here are some of the factors that could play a role:

Blood Type

Not surprisingly—since, after all, mosquitoes bite us to harvest proteins from our blood—research shows that they find certain blood types more appetizing than others. One study found that in a controlled setting, mosquitoes landed on people with Type O blood nearly twice as often as those with Type A. People with Type B blood fell somewhere in the middle of this itchy spectrum. Additionally, based on other genes, about 85 percent of people secrete a chemical signal through their skin that indicates which blood type they have, while 15 percent do not, and mosquitoes are also more attracted to secretors than nonsecretors regardless of which type they are.