Mosquitoes can be a constant pain if you are new to an area or on vacation in a hotter climate than you are used to. In some places they even carry one of the biggest worldwide killers in terms of diseases, in malaria. So knowing why they are attracted to humans and how you can stop them from wanting to feed on you can be very important. There are in fact several things that attract mosquitoes to humans. Rather then just them being able to smell our sweat, although this is important as well. They in fact have complex sight and smell senses and can detect a multitude of chemicals that most creatures cant to aid them in finding their prey.
First of all in close proximity mosquitoes can detect higher temperatures than the background levels. This means that even if a human was odorless then a mosquito near to them could tell they were there. So even if you have just showered and then gone to bed, meaning you were still and relatively odorless, you can still easily get bitten. This is also how they detect other warm blooded animals that don't give off as many chemicals as humans do that they can smell.
During the daytime when perhaps a hot temperature can make it hard to pick out people against other objects. Mosquitoes can also use motion detection as a means of attraction. If they see a warm object moving around then this tells them that it is most likely alive. And they are in turn attracted to it. This is why you can occasionally find mosquitoes landing on inanimate moving objects such as slow moving cars. In nature of course the only warm things that move are alive and are potential prey.
Most importantly mosquitoes can smell several chemicals that humans produce naturally, particularly when they are sweating more than usual. They can detect carbon dioxide in the air that we breathe out. They can also smell the bacteria that cause body odor as they break down in our sweat. If you are used to a hot climate, then you will find that you are bitten less because you sweat less. A tourist however use to much colder climates will sweat a lot more, and so will attract more mosquitoes. It is very rare to see a local person in most places that gets bitten a lot. Or if they do their body is used to this happening, and their bites don't welt up and become itchy.
Mosquitoes can also detect lactic acid, and even the tiny amounts of blood and protein that is excreted in our sweat and through our pores. So someone who is pregnant,takes steroids, or is significantly overweight will be more attractive to mosquitoes. This is because they all release more than usual of the chemicals that mosquitoes use to detect humans.
In terms of getting rid of mosquitoes there are several ways that can be effective. Firstly you can use repellent and anti mosquito traps, which to a degree work well. Of course making sure you are covered up and avoiding stagnant water and swamps works just as well during the daytime. At night and in the house in general mosquito nets and screen doors will protect you quite well as well.
To eradicate them entirely from your land you first need to locate the source that they are breeding from. It will inevitable be a stagnant or overgrown pool of water, or boggy ground. Drainage is the best way to be sure you are rid of them once and for all. But you can also buy chemical mixtures to pour into the water that kill the larvae without harming other pond-life as well.