Several factors make some people more attractive to mosquitoes than others. First, mosquitoes are drawn to carbon dioxide, and some people give off more of it naturally (especially if they're sick or drinking alcohol). Mosquitoes are also drawn to perspiration -- more so to stale sweat than fresh sweat, interestingly -- and to dark colors. So dress accordingly!
When it comes to repellents, the gold standard of protection is DEET. It's a synthetic compound that blocks mosquito bites for five to six hours, and it's available in various concentrations. But while DEET has been deemed safe by most regulatory organizations, some people have raised health concerns because it's fat-soluble and the body isn't able to metabolize it. I use it myself, but I advise being extra-careful with children and applying lower concentrations on them.
Some plant-based repellents have the same effect as DEET -- these feature ingredients such as eucalyptus and citronella. The one downside: They only protect for about 30 minutes. So if you're going to use them, remember to be vigilant about reapplying.
