Puerto Vallarta, Mexico - It's Summer in the tropics, and you know what that means... Mosquitoes! Puerto Vallarta's rainy season means it's mosquito season, too. The little buggers are not just annoying, but also carry diseases like Dengue and Chikungunya. But why do they bite some people more than others?

Mosquitoes exhibit blood-sucking preferences, say the experts. An estimated 20 percent of people, it turns out, are especially delicious for mosquitoes, and get bit more often on a consistent basis. And though researchers have yet to pinpoint what mosquitoes consider an ideal hunk of human flesh, they do know that genetics account for a whopping 85% of our susceptibility to mosquito bites, whether it's expressed through blood type, metabolism, or other factors.

Here are some of the factors that could play a role:

Blood Type

Not surprisingly — since, after all, the reason mosquitoes seek out human blood is because our blood enables their eggs to become fertile. Most mosquitoes seek out certain blood types and certain characteristics when choosing their prey. If you have Type O Blood, you are twice as likely to be bitten by mosquitoes than those with Type A. People with Type B blood fell somewhere in the middle of this itchy spectrum.

Carbon Dioxide

Mosquitoes can detect carbon dioxide from as far as 75 feet away. We all emit carbon dioxide, but the more carbon dioxide you emit, the more likely a mosquito will bite you. Adults emit more carbon dioxide than children, so in general, adults are more likely to be bit than children. Also people who exhale more of the gas over time — generally, larger people and smokers — have been shown to attract more mosquitoes than others.

Exercise and Metabolism

Scent is the primary indicator for mosquitoes that a human target is within striking distance. In addition to carbon dioxide, 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. Because strenuous exercise increases the buildup of lactic acid and heat in your body, it likely makes you stand out to the insects.

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. In a 2011 study, scientists found that having large amounts of a few types of bacteria made skin more appealing to mosquitoes. Surprisingly, though, having lots of bacteria but spread among a greater diversity of different species of bacteria seemed to make skin less attractive. This also might be why mosquitoes are especially prone to biting our ankles and feet — they naturally have more robust bacteria colonies.

Secretions

About 80% of us are "secretors," or people who secrete compounds known as saccharides and antigens through their skin and indicate blood type. Mosquitoes are magnets for secretors. Once again, your classification as a secretor or non-secretor is determined by your biology and there isn't anything you can do to put yourself in the non-secretor category.

Drinking Alcohol and Higher Body Temperature

According to one study, drinking just one can of beer or one mixed drink drastically increases your chances of being bit by a mosquito. This is because drinking alcohol increases your body temperature and increases the amount of ethanol excreted in sweat. Additionally, some people naturally have higher body temperatures than other people. Mosquitoes are drawn to warmer blood.

Pregnancy

In several different studies, pregnant women have been found to attract roughly twice as many mosquito bites as others, likely a result of the fact the unfortunate confluence of two factors: They exhale about 21 percent more carbon dioxide and are on average about 1.26 degrees Fahrenheit warmer than others.

Clothing Color

Mosquitoes use vision (along with scent) to locate humans, so wearing colors that stand out (black, dark blue or red) may make you easier to find. To reduce your risk of getting bit, wear lighter colors.

Natural Repellents

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 repellents. Using chromatography to isolate the particular chemicals these people emit, scientists at the UK's Rothamsted Research lab have found that these natural repellers tend to excrete a handful of substances that mosquitoes don't seem to find appealing. Eventually, incorporating these molecules into advanced bug spray could make it possible for even a Type O, exercising, pregnant woman in a black shirt to ward off mosquitoes for good.

In the meantime, for those who do not want to bombard their bodies with toxic chemicals that pollute themselves and the environment, HERE is a list of some popular natural repellents. We are not guaranteeing results, but we hope one of these will work for you.