She makes the trip up to Wisconsin and Minnesota every year, and she always comes home the same way: carry-on packed with aged cheddar, mozzarella sticks, fresh cheese curds, and a stack of frozen Carbones pizzas she cannot get anywhere near south Florida. TSA pulls her aside almost every single time for extra screening, but she is used to it. Her last trip started the same, but she was not prepared for the bomb squad. She shared her story on Reddit's TSA community.
She had about 20 blocks of cheese and several spreadable cheese spreads tucked into her carry-on when she hit security at Minneapolis-St. Paul Airport. Getting flagged for extra screening was nothing new, but getting swabbed was. This time, agents carefully wiped down each individual block of cheese and kept every swab labeled separately, which she described as strange enough to make her think something had already come back positive. She was right.
Four swabs came back flagged. The culprits were mostly cheese ends, the trimmed outer pieces of larger blocks that get packaged together, along with all of her cheese spreads, including a Gruyere she had bought just two hours earlier. The spreads were a separate issue entirely: anything spreadable, including cream cheese, peanut butter, hummus, or soft cheese, falls under TSA's liquids and gels rule and cannot travel in a carry-on unless it is under 3.4 ounces.
She tried to voluntarily hand over the flagged items and move on. Agents told her that was not an option and that all of her bags would need to be fully re-screened. Then a supervisor arrived, and after a brief conversation between the security agents, she was cleared to leave, minus the cheese ends and every one of her spreads. Luckily, her six frozen pizzas, packed in the same bag, passed without incident.
The Reddit thread filled up with people who had been through something similar, and the explanations were more specific than anything she had gotten from TSA at the checkpoint.
Several commenters pointed to nitrates as the most likely explanation. Nitrates are used as preservatives in packaged cheese, especially aged and processed varieties, and they share a chemical profile with compounds found in some explosives. Cheese ends, which are handled more often and may have had more surface contact than a sealed block, are particularly likely to yield a positive swab result.
A former TSA officer explained the protocol: once an item tests positive at the explosives trace detector, a regular officer cannot simply retest it and wave it through. Clearing the alarm requires an explosives specialist, and not every airport has one available at all hours. Without a specialist on hand, the only real options are to check the item or voluntarily surrender it.
Another user noted that glycerin, found in many hand soaps and lotions, produces the same kind of false positive, and that anyone who has used glycerin-based products before going through security risks, triggering the machine even without any food involved.
The explosives trace detector is not looking for bombs. It screens for individual chemical compounds that appear in both explosive materials and a wide range of everyday products: food preservatives, fertilizers, hand lotions, certain medications, and even some cleaning products. A positive result is a chemical match, not a confirmed threat, which is why the response involves a specialist rather than an immediate evacuation.
Understanding that distinction makes the food rules at the checkpoint a lot easier to navigate. Solid foods, including block cheese, whole fruit, sandwiches, baked goods, and anything that holds its shape without its container, are generally allowed in a carry-on. The line is drawn at anything that does not hold its shape, which is where the liquid and gel rule applies. Peanut butter, yogurt, hummus, jam, spreadable cheese, and similar items must be 3.4 ounces or less to make it through.
Frozen food works differently. If something is frozen solid at the checkpoint, TSA will typically allow it through, even if it would otherwise be considered a gel or liquid. The catch is that airports in warm climates can thaw things faster than expected, and a bag that went through security frozen may arrive home as a congealed mess.
If you are the kind of person who travels home with food in your carry-on, which is one of the genuinely great things about going somewhere new, there are a few rules worth keeping straight. Spreadable foods belong in checked bags or in containers under 3.4 ounces. Frozen solids are allowed at the checkpoint, but may not remain frozen. And if you use glycerin-based soap, handle fertilizer, or take certain medications, wash your hands thoroughly before you go through security.
If the swab machine flags your cheese anyway, ask for a supervisor and ask what your options are. It happens more often than most people realize, and in most cases, it is a false positive from a preservative or a surface chemical, not an actual threat. The Wisconsin cheese was worth the trip, but next time, just put the spreads in the checked bag.
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