If you seem to be the target of bloodsucking attention, there are two biological systems you can blame — your microbial flora, and/or your immune system. Your particular mix of skin bacteria play a big role in determining how well mosquitoes can smell you (and whether you smell delicious). Meanwhile, your immune system controls your allergic response — or lack thereof — to mosquito bites. If you never get red welts to go with the biting, it’s easy to think that you’re not getting bitten as often as someone who does.