Mushroom Swiss King: Allergens at a Glance
The honest verdict
Mushroom Swiss King · Burger King
The Mushroom Swiss King is a Burger King burger featuring a flame-grilled beef patty, a sesame seed bun, Swiss cheese, sautéed mushrooms, and mayonnaise. The allergen profile is anchored by wheat from the bun, milk from the Swiss cheese and sauce, egg from the mayonnaise, and soy from the mayonnaise and cooking oil. Sesame is present on the bun. Peanut, tree nut, fish, and shellfish are not typical ingredients. Cross-contact via shared grill surfaces and fryers is possible. Burger King's allergen information varies by location and changes over time — always confirm with your specific restaurant before ordering.
Allergen details change and vary by location. This is a general guide — always confirm with the restaurant before ordering. Not official or medical advice.
Key facts
Burger King's sesame seed bun makes the Mushroom Swiss King a direct source of both wheat and sesame allergens.
Swiss cheese and mayonnaise are the primary sources of milk and egg allergens in this burger.
Burger King flame-grills patties on shared broiler surfaces, creating cross-contact risk across menu items.
Every major allergen, one clear grid
Each of the nine major allergens marked for Mushroom Swiss King at Burger King — Contains, May contain (cross-contact or varies), or Free. Anything we couldn't confirm defaults to "may contain," because a shared kitchen can't be ruled out without the restaurant's official menu.
- MilkContains
Swiss cheese is a dairy product and contains milk. The mushroom sauce may also contain milk or cream. This is a primary allergen in this burger.
- EggContains
Mayonnaise is a standard ingredient on Burger King burgers and contains egg. The mushroom sauce may also contain egg.
- Wheat / GlutenContains
The sesame seed bun is wheat-based. This is a primary allergen in this burger.
- SoyMay contain
Mayonnaise typically contains soybean oil. Burger King's cooking oil may also be soy-based. Highly refined soy oil is FDA-exempt from allergen labeling and tolerated by most with soy allergy. Those with severe soy sensitivity should confirm the oil type used.
- PeanutFree
Peanut is not a typical ingredient in Burger King burgers or toppings. Cross-contact is very unlikely.
- Tree NutFree
Tree nuts are not an ingredient in the Mushroom Swiss King or its components.
- FishFree
Fish is not an ingredient in this burger. Cross-contact is unlikely unless the restaurant prepares fish items on shared surfaces.
- ShellfishFree
Shellfish is not an ingredient in this burger. Cross-contact is unlikely.
- SesameContains
The bun is typically a sesame seed bun. Sesame is a direct ingredient. Some locations may offer a plain bun without sesame — ask the restaurant.
“May contain” means cross-contact is possible or the answer varies by location — not that the allergen is a listed ingredient. For a severe allergy, treat “may contain” the same as “contains” until the restaurant confirms otherwise.
Small changes that remove an allergen
Simple modifications that can take an allergen off your mushroom swiss king. Always name your allergy when you order and ask staff to confirm — a modification only helps if the kitchen prepares it separately.
Order without the bun (lettuce wrap or bunless)
Order without Swiss cheese
Order without mayonnaise
Request a plain bun without sesame seeds
A modification lowers exposure but doesn't erase cross-contact from shared fryers, grills, or prep surfaces. For a severe allergy, confirm the prep with a manager before you eat.
Read this before you order
Cross-contact & severe allergies
A “free of” mark on the grid above means the allergen isn't an ingredient — it doesn't mean the item was made in an allergen-free kitchen. Two things matter most:
Shared fryers & equipment
Burger King flame-grills patties on a shared broiler that cooks multiple menu items. The same grill surface may contact buns, cheese, and other allergens. Fryers are shared across menu items including chicken, fish, and onion rings. Cross-contact with wheat, milk, egg, soy, and fish is possible through shared equipment and preparation surfaces.
If your allergy is severe
For anaphylactic allergy to wheat, milk, egg, soy, or sesame, confirm preparation practices with your specific Burger King location before ordering. The Mushroom Swiss King is not guaranteed safe for any of these allergens without restaurant-level confirmation. Carry your epinephrine auto-injector. If you cannot confirm preparation details, consider a simpler menu item with fewer components.
This guidance is general and can't account for how any single location prepares your food. The restaurant's staff and official allergen menu are the final word — when in doubt, ask, or choose something else.
❓Frequently Asked Questions
Yes. The Swiss cheese is a dairy product and contains milk. The mushroom sauce may also contain milk or cream. This burger is not dairy-free as served. Removing the cheese reduces but does not eliminate the dairy risk if the sauce contains milk. Ask the restaurant about the sauce ingredients.
No. The sesame seed bun is wheat-based, making this burger a direct source of gluten. Ordering the burger without the bun (lettuce wrap or bunless) removes the wheat, but cross-contact from shared grill surfaces where buns are toasted may still introduce trace gluten. Confirm with the restaurant whether they can prepare it on a clean surface.
Yes, the bun is typically a sesame seed bun. Sesame is a direct ingredient. Some Burger King locations may offer a plain bun without sesame seeds upon request. Ask the restaurant about bun options if you have a sesame allergy.
Both share the same bun, beef patty, and mayonnaise base. The Mushroom Swiss King adds Swiss cheese (milk) and sautéed mushrooms, while the Whopper adds American cheese (milk), lettuce, tomato, pickles, ketchup, and onions. The Mushroom Swiss King has a simpler vegetable profile but the same core allergens: wheat, milk, egg, soy, and sesame.
Removing the Swiss cheese removes the most obvious dairy source, but the mushroom sauce may still contain milk or cream. The mayonnaise is egg-based but typically dairy-free. Ask the restaurant whether the mushroom sauce contains dairy. If it does, request the burger with just mushrooms and no sauce, or substitute a dairy-free condiment.
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Read moreFind out which foods you actually react to
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Please verify before ordering
Allergen info changes and varies by location
Recipes, suppliers, and preparation methods change often and differ between locations, so the details here can go out of date or not match your specific Burger King restaurant. Always confirm directly with the restaurant and check its official allergen menu before ordering. This page is a general research summary — it is not official information from Burger King, and it is not medical advice. If you have a food allergy, decisions about what is safe to eat should be made with the restaurant and, where relevant, your healthcare provider.