It has to do with the natural odor your body gives off.

Scent.

some people smell more appetising than others. If that bitee is you, then you have natural mosquito-attracting perfume than others...

Pharamones!

Alot of it has to do with blood sugar. If you have alot of sugar in your bloody, they'll bite

Yep. Evidence suggests there is actually two separate factors: the particular scent your breath or your body gives off that may be attractive to mosquitoes, and your body's own ability to produce a masking odor. A theory that is quickly gaining credence is that people who don't get bitten actually produce more of a 'masking' odor to disguise their attractiveness. In fact, scientists are now leaning more toward the masking chemical that repels, and are putting less focus on the 'attractive' odor. Quote: "Research student James Logan has found that some people give off "masking" odours that prevent mosquitoes from finding them. His research builds on earlier studies on cattle, led by Rothamsted's Professor John Pickett, which showed that the number of flies on a herd depended on certain cows being present. The scientists found these key unattractive individuals gave out different chemical signals from the other cows. When these individuals were moved to another field the number of flies afflicting the previous herd increased. Their results suggest that differential attractiveness is due to compounds in unattractive individuals that switch off attraction either by acting as repellents or by masking the attractant components of human odour. This theory differs from that of other research groups who have suggested that unattractive individuals lack the attractive components" http://www.medicalnewstoday.com/articles/19125.php At the other end of the scientific spectrum are those that believe that certain individuals are more attractive to mosquitoes than others. Theories as to which compounds are attractive to the bugs abound, but the amount of carbon dioxide emitted from your breath is a popular theory. Mosquitoes are drawn to you from many miles away based on a single breath. The greater the amount of carbon dioxide expelled in each breath, the more attractive you become. Pregnant women are high on the hit list, for this reason. Expectant mothers exhale an average of 21% more carbon dioxide than normal, plus they are 1-2 degrees warmer. Both are very attractive to mosquitoes. Recent studies have found that blood type may have something to do with it, as well. Type 'O' individuals were more commonly preyed upon than other individuals. http://scienceline.org/2007/09/10/ask-knight-mosquitoes/ In the end, research is ongoing, but it appears we are getting closer to an answer. Your best defense seems to be hanging close to those that are rarely bitten, so as to help mask your own smell, or to always invite the poor soul who is always bitten, thus providing a preferred feeding ground. For myself, my wife is the ultimate meal for any biting insect. If she's nearby, no bug wants to nosh on me. I don't blame them. I'd much rather snack on her, too! ;-)

Different blood composition. Some people have more of one thing and less of another. For instance some peoples blood has more sodium. Others may have more iron.