You come in from outside covered with itchy red mosquito bites, only to have your companions say they have none. An estimated 20 percent of people are especially delicious for mosquitoes, and get bitten more often on a consistent basis.

And while scientists don’t yet have a cure, other than preventing bites with insect repellent (which some mosquitoes can become immune to over time), they do have a number of ideas about why some of us are more prone to bites than others:

Blood type
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.

Carbon dioxide
People who simply exhale more of the gas over time—generally, larger people—have been shown to attract more mosquitoes.

Exercise and metabolism
Mosquitoes find victims at closer range by smelling the lactic acid, uric acid, ammonia and other substances expelled via their sweat, and are also attracted to people with higher body temperatures.

Skin bacteria
Other research has suggested that the particular types and volume of bacteria that naturally live on human skin affect our attractiveness to mosquitoes.

Just a single 12-ounce bottle of beer can make you more attractive to the insects, one study found.

Pregnant women have been found to attract roughly twice as many mosquito bites as others.

Clothing color
Colors that stand out (black, dark blue or red) may make you easier to find

Underlying genetic factors are estimated to account for 85 percent of the variability between people in their attractiveness to mosquitoes

Natural repellants
Some researchers have started looking at the reasons why a minority of people seem to rarely attract mosquitoes in the hopes of creating the next generation of insect repellants.