Some people seem to eat questionable chicken without consequences, while others get taken down by a suspect sandwich. If you’ve ever wondered why food poisoning seems to “choose” its victims, you’re not alone—and as it turns out, science has a few fascinating theories.
Gut bacteria isn’t equal in everyone.
Your gut is home to trillions of microbes that help with digestion and protect you from harmful invaders. But everyone’s microbiome is a little different, and some are better equipped to fight off bacteria like salmonella or E. coli than others.
If your gut ecosystem is thriving—thanks to a good diet, probiotics, or just plain luck—you might have a stronger defence system in place. But if your gut health is out of balance, you’re more vulnerable to getting knocked out by something your friend barely noticed.
Some immune systems are just more reactive.
Your immune system’s job is to identify threats and respond, but how aggressively it does that can vary wildly between people. One person’s immune system might treat bad mayonnaise like a minor annoyance, while another’s sees it as a full-blown crisis.
In some cases, a stronger immune reaction can actually make symptoms worse—think vomiting, diarrhoea, or fever. It’s not that the food was necessarily more contaminated for one person, but that their body fought harder (and louder) against it.
Stomach acid plays a bigger role than you’d think.
Stomach acid is one of your first lines of defence against foodborne pathogens. If your stomach acid levels are high, it’s like sending unwanted microbes through a meat grinder before they can get further into your system. However, if your acid levels are lower—whether naturally, due to age, or because you take antacids—you’re less protected. That means bacteria have an easier time surviving the trip and causing chaos once they reach your intestines.
Genetics can influence how sensitive you are.
Some people are naturally more sensitive to certain toxins due to their genes. For example, some individuals have mutations that affect how their body processes histamines in spoiled fish or reacts to specific bacterial proteins. So, when you get food poisoning and someone else doesn’t, part of it could simply come down to your DNA. It doesn’t mean you’re weak—it just means your body notices things others might not.
Pre-existing health conditions matter.
People with chronic conditions like diabetes, IBS, or autoimmune diseases often have a harder time fighting off infections. Their systems are either already under strain or more prone to inflammation when something goes wrong. That doesn’t mean they’ll always get sick from risky food, but it does mean that when something slips past their defences, the symptoms can hit harder and last longer than they would for someone without those conditions.
You might be eating the same food, but not the same amount.
Food poisoning isn’t always about whether bacteria were present—it’s often about the dose. The more contaminated food you eat, the higher the chance your body gets overwhelmed by it. If you took the last big bite of that sketchy chicken wrap or went back for seconds on dodgy prawns, you might just have consumed more of the harmful stuff than your friend did. That difference alone can tip the scales.
Timing makes a surprising difference.
If you eat risky food on an empty stomach, bacteria have a clearer path to your intestines. But if you’ve already eaten a full meal, your digestive system slows everything down and gives your body more time to mount a defence. So, two people eating the same food could have completely different outcomes depending on when and how they ate it. Timing doesn’t always protect you, but it definitely influences how fast and hard the bacteria can act.
Hydration affects your body’s response.
Being dehydrated can make your system more fragile and less efficient at flushing out toxins. That’s part of why hangovers and food poisoning feel similar—both leave your body struggling to deal with stress while low on fluid. If your friend was sipping water all day, and you were running on three coffees and no lunch, your body is more likely to take a hit if bacteria shows up. Hydration supports every part of the immune response, even the gross bits.
Age plays a bigger role than most people realise.
Children and older adults are generally more vulnerable to foodborne illness. Their immune systems are either still developing or have started to slow down, meaning harmful bacteria have an easier time gaining ground. Even healthy adults experience changes in gut flora and digestion as they age, which can impact how well they handle contaminated food. So it’s not just about luck—it’s also about biology catching up with you.
Stress can literally mess with your digestion.
If you’re anxious or under pressure, your digestive system can become more sensitive. Stress hormones slow digestion, weaken your gut lining, and reduce stomach acid—basically, they set the stage for bacteria to take hold more easily. In other words, if you’re on edge while eating that suspect buffet plate, you might be more prone to symptoms than someone who’s calm and relaxed. It’s a weird example of mind-body connection, but science says it checks out.
Some people have developed immunity.
In areas with frequent food contamination, people sometimes build up partial immunity to local bacteria. This doesn’t make them invincible, but it does mean they might have fewer or milder symptoms after exposure. If someone grew up around a certain type of cuisine or hygiene level, their system may be more familiar with the bacteria involved. A tourist eating the same food might get flattened, while a local shrugs it off.
Bad luck still plays a role.
Even with all the science, sometimes food poisoning really does come down to random chance. One bite might contain a dangerous clump of bacteria, while another is totally fine—despite coming from the same plate. No matter how strong your gut is or how healthy you feel, sometimes it’s just unlucky positioning. You hit the jackpot of germs, and your friend didn’t. Not everything has a neat biological reason, but at least now you know the odds.
Your recovery speed might be hiding the evidence.
It’s possible that multiple people did get food poisoning, but only some noticed. If your body clears the bacteria quickly or reacts mildly, you might just feel a bit off and forget about it by morning. Meanwhile, someone else could end up out of commission for two days with the same exposure. So it’s not always about who got hit—it’s also about who felt it enough to notice.
