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Foodborne hazards and allergen cross-contact
A foodborne hazard is anything in food that can hurt the person eating it. The FDA Food Code defines a hazard as biological, chemical or physical (1-201.10), and allergens get rules of their own, because a trace of the wrong protein can send a guest to the emergency room.
- ExamPFH
- Topic weight10%
- Questions here15
- UpdatedOct 14, 2026
On this page 6 sections
Three types of foodborne hazard
| Type | What counts | How it shows up on a line | What stops it |
|---|---|---|---|
| Biological | Living germs and the toxins some of them make | Juice from a raw chicken tray dripping onto sliced tomatoes below it | Raw stored under ready-to-eat food, cooking to temperature, washed hands |
| Chemical | Cleaners, sanitizers, pesticides, metals from the wrong container | Degreaser sprayed on the hood above open bins of breading | Using it exactly as the label says, with open food covered or moved first |
| Physical | Objects that can cut, choke or break a tooth | A bandage, a twist tie, a fish bone, a sliver from a worn can opener | Covered cuts, tidy prep areas, equipment kept in repair |
FDA Food Code 2022, 1-201.10, definition of hazard.
Allergens and cross-contact
Since the 2022 Food Code there are nine major food allergens, the Big 9 (1-201.10):
- milk
- eggs
- fish
- crustacean shellfish
- tree nuts
- wheat
- peanuts
- soybeans
- sesame, the newest on the list
Cross-contact is allergen protein moving from one food to another: a fryer shared by shrimp and fries, a knife that cut a peanut-butter sandwich, a glove that just handled cheese. Heat doesn't break the protein down the way it kills germs, so the fix is clean tools, a clean surface and fresh ingredients. The page on the Big 9 allergens takes them one at a time.
Scraping the seeds off a bun for a guest with a sesame allergy is a shortcut that fails: the protein is already on the bread. A new bun and a clean spatula fix it.
Germs make the same trip from surface to food, and that has its own name: cross-contamination. The germs themselves are covered under foodborne illness.
Spot the hazard
Several of these are set at a buffet or a salad bar, where guests become part of the problem.
Each question is a chit, an order ticket. Answer it and it flips to show why every option is right or wrong.
No. 01
Which type of contamination involves harmful substances like cleaning chemicals getting into food?
Pick one. The chit flips to a note on every option.
Notes on No. 01
- A
Cross-contamination Cross-contamination is how germs move from one surface or food to another, not a type of substance.
- B
Physical contamination Physical contamination means objects like glass, metal, or hair.
- C
Biological contamination Biological contamination comes from living things like bacteria, viruses, and parasites, and the toxins they make.
- D
Chemical contamination Correct: Cleaners, sanitizers, pesticides, and other non-food chemicals that get into food are chemical contamination.
- A
No. 02
What is an example of physical contamination in food?
Pick one. The chit flips to a note on every option.
Notes on No. 02
- A
Bacteria Bacteria are a biological hazard, not a physical one.
- B
Cleaning chemicals Cleaning chemicals are a chemical hazard.
- C
Glass shards Correct: Glass is a physical hazard, a foreign object that can cut or choke, and no amount of cooking fixes it.
- D
Food allergens Allergens are proteins in the food itself that cause reactions; they are not a foreign object.
- A
No. 03
Which of the following is an example of biological contamination?
Pick one. The chit flips to a note on every option.
Notes on No. 03
- A
Viruses Correct: Viruses like Norovirus and Hepatitis A are pathogens, and pathogens are what make up biological contamination.
- B
Metal shavings Metal shavings are physical contamination.
- C
Hair Hair is a physical contaminant, though it can also carry germs.
- D
Cleaning solutions Cleaning solutions are chemical contamination.
- A
No. 04
Which naturally occurring toxin is commonly found in raw kidney beans?
Pick one. The chit flips to a note on every option.
Notes on No. 04
- A
Aflatoxin B1 Aflatoxin is made by molds on grains and nuts such as corn and peanuts, not by beans.
- B
Phytohemagglutinin Correct: Raw or undercooked kidney beans contain phytohemagglutinin; soaking and boiling them thoroughly destroys it.
- C
Alpha-solanine Solanine is found in green or sprouted potatoes.
- D
Tetrodotoxin Tetrodotoxin is the toxin in pufferfish.
- A
No. 05
Which food is most likely to contain methylmercury contamination?
Pick one. The chit flips to a note on every option.
Notes on No. 05
- A
Fresh fruits Fruit isn't a source of methylmercury.
- B
Dairy products Dairy products are not a meaningful source of methylmercury.
- C
Large predatory fish Correct: Methylmercury builds up through the food chain, so big long-lived fish like swordfish, shark, and king mackerel carry the most.
- D
Root vegetables Root vegetables aren't a source of methylmercury.
- A
No. 06
A dishwasher rinses out an empty sanitizer jug and offers it to the line for storing fryer oil. What's the rule?
Pick one. The chit flips to a note on every option.
Notes on No. 06
- A
Use it once it's rinsed three times Rinsing can't be trusted to remove every trace of chemical, which is why the rule bans the swap outright.
- B
Relabel it as fryer oil, then use it A new label doesn't remove leftover chemical; the jug can still contaminate the oil.
- C
Turn it down; chemical jugs never hold food Correct: A container that ever held a toxic chemical may never be used to store, carry, or serve food.
- D
Sanitize it first, then fill it with oil Sanitizing a sanitizer jug changes nothing; any container that held chemicals stays off-limits for food.
- A
No. 07
What personal protective equipment (PPE) should be worn when mixing sanitizing chemicals?
Pick one. The chit flips to a note on every option.
Notes on No. 07
- A
Regular cloth kitchen gloves and an apron Cloth soaks up chemicals and holds them against the skin.
- B
Just an apron over the uniform An apron protects clothing but leaves hands and eyes open to splashes.
- C
No protection if mixing in a sink Mixing in a sink still splashes, and concentrated sanitizer can burn skin and eyes.
- D
Chemical-resistant gloves and eye protection Correct: Concentrated sanitizer can burn skin and eyes, so follow the label and the safety data sheet, which usually call for chemical-resistant gloves and eye protection.
- A
No. 08
What is the most effective way to prevent chemical contamination?
Pick one. The chit flips to a note on every option.
Notes on No. 08
- A
Regular cleaning of all surfaces Cleaning is when chemicals get used near food, so on its own it can add risk rather than remove it.
- B
Training staff on food safety Training matters, but what physically keeps chemicals out of food is labeling them and storing them away from it.
- C
Holding food at the right temperature Temperature control fights bacteria; it does nothing about chemicals.
- D
Proper labeling and separate storage Correct: Labeled containers prevent mix-ups, and storing chemicals apart from and below food keeps spills and splashes off it.
- A
No. 09
At the salad bar, a guest comes back for seconds holding the plate they already ate from. What should the server do?
Pick one. The chit flips to a note on every option.
Notes on No. 09
- A
Let them refill it; it's their own plate A used plate carries the guest's saliva and germs back to the shared food and serving utensils.
- B
Hand them a clean plate for the refill Correct: Guests may not use a soiled plate to get more food from a self-service bar, so hand them a clean one.
- C
Wipe the plate with a napkin, then refill A napkin wipe doesn't clean or sanitize the plate, so germs still reach the serving utensils.
- D
Refill it if they also take a clean fork A clean fork doesn't help; the soiled plate is what touches the serving utensils and the display.
- A
No. 10
How should serving utensils be stored during service?
Pick one. The chit flips to a note on every option.
Notes on No. 10
- A
Tucked in server aprons for quick reach Aprons carry germs from hands and clothing onto the utensil.
- B
In a pan of standing room-temp water Room-temperature water lets bacteria grow; a utensil may sit in water only if it stays at 135°F or above, or runs continuously.
- C
Lying on the counter next to the pans A bare counter can contaminate the part of the utensil that touches food.
- D
With handles above rim or in clean container Correct: Utensils go in the food with handles sticking up, or in a clean, protected spot, so hands touch only the handle.
- A
No. 11
How should TCS foods be set out on a buffet line?
Pick one. The chit flips to a note on every option.
Notes on No. 11
- A
Any order, as long as the line looks full Looks don't matter; what matters is temperature, time, and keeping foods from touching.
- B
One serving utensil shared down the whole line A shared utensil carries food and allergens from one pan to the next.
- C
Small batches with their own utensils, replaced fully Correct: Small pans spend less time out, each TCS food (formerly PHF) gets its own utensil, and a pan is swapped out whole rather than topped off.
- D
Large batches, topped off with fresh food as needed Topping off mixes older food with new, so the oldest food never leaves the pan.
- A
No. 12
Which symptom is most indicative of a chemical contamination incident?
Pick one. The chit flips to a note on every option.
Notes on No. 12
- A
Immediate burning sensation Correct: Chemicals act fast, often within minutes, causing burning in the mouth or throat or vomiting, unlike germs, which take hours or days.
- B
Headache the next day A headache the next day is too late and too vague to point to a chemical.
- C
Nausea after 12 hours Nausea 12 hours later fits a bacterial illness better than a chemical.
- D
Fever after 24 hours Fever a day later points to an infection, not a chemical.
- A
No. 13
How should self-service food displays be monitored?
Pick one. The chit flips to a note on every option.
Notes on No. 13
- A
Checked by the closer at the end of the night One check at closing finds problems hours after guests ate the food.
- B
Only when an item runs low and needs refilling Refilling is not a safety check, and topping off hides how long food has been out.
- C
Watched by staff, with temps checked during service Correct: Self-service food must be watched by trained staff, who check temperatures during service and fix guest mishandling right away.
- D
Once per day before the doors open One check before opening misses everything that happens during service.
- A
No. 14
How should prepared sandwiches be wrapped for service?
Pick one. The chit flips to a note on every option.
Notes on No. 14
- A
Stacked together in bulk containers Bulk stacking lets sandwiches touch, spreading allergens and juices between them.
- B
In plain paper bags, several per bag Several sandwiches in one bag can share fillings and allergens.
- C
Individually in food-grade wrap Correct: Wrapping each sandwich protects it from handling and lets each one carry its own label and allergen information.
- D
Unwrapped on a tray for the case Unwrapped sandwiches are open to sneezes, hands, and dust in the case.
- A
No. 15
Which type of food processing creates the highest risk for chemical contamination?
Pick one. The chit flips to a note on every option.
Notes on No. 15
- A
Freezing food in the walk-in Freezing doesn't add chemicals to food.
- B
Packaging food for takeout Packaging carries a small risk if it isn't food-grade, but it isn't the main source.
- C
Equipment cleaning and sanitizing Correct: Cleaners and sanitizers are used right on food-contact surfaces, so poor rinsing, wrong mixing, or spills can leave residue on food.
- D
Cooking food on the line Cooking is a heat step; it doesn't add chemicals unless something is misused.
- A
Nothing matches both filters. Clear one of them.
Hazards and allergens: short answers
When did sesame become a major food allergen?
The FDA Food Code 2022 lists sesame as the ninth major food allergen (1-201.10); the older list had eight. The 2026 edition keeps the same nine (FDA summary of changes, as of October 2026).
Is cross-contact the same thing as cross-contamination?
No. Cross-contamination moves germs; cross-contact moves allergen protein. Cooking kills germs only in food that still gets cooked, and it never removes an allergen, so on ready-to-eat food neither one can be fixed after the fact. Separation and clean tools prevent both.
Sources
- FDA Food Code 2022 — 1-201.10 hazard and major food allergen; 7-102.11; 7-201.11 checked Oct 13, 2026
- FDA, summary of changes in the 2026 Food Code — sesame stays on the 2026 allergen list checked Oct 13, 2026