Why do mosquitoes feast on you and ignore your friend?

Mosquitoes bite you more than your friend because your body advertises itself differently, and a surprisingly large part of that advertising is genetic. Twin studies suggest your attractiveness to mosquitoes is roughly 60 to 80% heritable, putting it in the same league as height. The signals that draw them, the carbon dioxide you exhale, the chemistry of your skin, and your body heat, are all shaped by genes you never chose. So if you have spent every monsoon convinced that mosquitoes single you out, you are not imagining it, and it was never about your 'sweet blood'.

It starts with your breath. Mosquitoes are essentially tiny carbon dioxide trackers. They can detect the plume of CO2 you exhale from several metres away and use it to lock onto a living target. Bigger bodies and higher metabolic rates exhale more, which is partly why adults get bitten more than small children, and why you become a beacon right after climbing a flight of stairs or finishing a workout. Some of your baseline output here is set by your build and metabolic rate, both of which carry a genetic signature. You cannot consciously change how much you breathe out, which is the first reason this feels so unfair.

Then your skin closes the deal. Up close, the real decider is the cocktail of chemicals your skin releases. Your body emits compounds like lactic acid, ammonia, and various fatty acids, and crucially, the community of bacteria living on your skin transforms your sweat into a specific personal scent that a mosquito reads like a name tag. Genes influence both your sweat composition and which bacteria flourish on you. People who naturally emit more of certain attractive compounds are simply easier to find. One well-known study found that people who were highly attractive to mosquitoes stayed that way consistently across repeated tests, which strongly suggests a stable, built-in chemical signature rather than the bad luck of a single evening.

This is the part that explains the dinner-table mystery. Two people sit side by side, eat the same food, drink the same water, and one gets bitten ten times while the other walks away untouched. The difference is not behaviour. It is the broadcast each body is putting out, and that broadcast is largely genetic.

Blood type may play a small supporting role. Some research suggests people with type O blood get bitten somewhat more than other blood groups, possibly because a majority of people secrete blood-type markers through their skin, giving mosquitoes another cue. The evidence here is softer and less consistent than the skin-chemistry findings, so it is best treated as a minor supporting actor rather than the lead. If you are type O and feel persecuted, the bigger story is still your skin and your breath, not your blood group alone.

Why do some people barely react to bites while others swell up? Worth separating two different things people lump together: how often you get bitten, and how badly you react. The swelling, itching, and redness after a bite are your immune system responding to proteins in mosquito saliva, and that response varies enormously from person to person. Someone can be bitten constantly yet barely react, while another person is rarely bitten but reacts dramatically to each one. So the friend who 'never gets bitten' may simply be getting bitten without the visible fuss. Both traits, attractiveness and reactivity, are individual to your biology.

What this means at your next outdoor dinner. You cannot rewrite your skin chemistry, but you can jam the signal. Repellents containing DEET or picaridin work by scrambling a mosquito's ability to read you, and they are the most reliable tools available regardless of your genetics. Covering exposed skin at dusk, when biting activity peaks, genuinely helps. And no, eating raw garlic or loading up on vitamin B will not build an invisible force field, because both have been tested and neither holds up. Standing fans on a balcony actually work better than most folk remedies, because mosquitoes are weak fliers and struggle against moving air while also losing your CO2 trail.

If you have spent your life believing mosquitoes love you specifically, you were right, and now you know it was never in your head. It was in your genes and on your skin. The takeaway: your appeal to mosquitoes is largely inherited and remarkably consistent across your life. You cannot change the broadcast your body sends out, but you can block the receiver with a proven repellent, smart timing, and a bit of moving air.