"Sometimes it's gone from hives or my throat has swelled up to where I almost can't breathe. There have been times where I've had to throw up or vomit," said Bryan Cook of Redondo Beach.
Serious reactions can lead to death. Cook is cautious all year long, but during the holidays, he is extra careful.
"You have potlucks and people bringing a variety of dishes together and it can be difficult to sit there and have to ask every person at the party, 'What is in this dish and what is in this dish?'" said Cook.
Dr. Katie Marks-Cogan says the top food allergens include milk, eggs, wheat, soy, peanuts, tree nuts and fish. Many are hidden in holiday meals.
"Green bean casserole often contain dairy and nuts, so maybe people can steam the green beans and top them with pumpkin seeds instead of with almonds," said Marks-Cogan.
In mashed potatoes, substitute with rice milk, olive oil or chicken broth.
"Always ask about the gravy. Gravy often contains wheat flour as a thickening agent," said Marks-Cogan.
Even if you keep everything separate and labeled on the table, there's always cross-contamination like mixing up nut-free cookies with other baked goods or mixing up serving spoons using them in more than one dish. Experts say if you have allergies, you have to educate your guests.
"If you are going to a holiday party and you have a food allergy, call ahead, speak of time and let the host know what your food allergies are," said Marks-Cogan.
Marks-Cogan also suggests printing out ingredient labels for every dish. Cook says he always goes into Thanksgiving well-prepared.
"Planning ahead is always important and coordinating with whoever is organizing any sort of event or potluck is definitely key.
Never be afraid to ask what's in your food.