In order to eat safely, practice the four principles: clean surfaces and fruits/vegetables, separate meats and seafood from other foods, cook to the right temperature, and cool or refrigerate food promptly – http://www.fightbac.org/food-safety-basics/the-core-four-practices/.
Food allergies happen when the immune system of the body reacts to the food as an antigen (something that’s not supposed to be there) and produces an allergic response. That response can be fairly mild, like itching, or severe, like anaphylaxis. If you know you are allergic to something, make sure to read warning labels, let a waiter know, read ingredients lists, and carry an epinephrine injector with you for emergencies.
Food intolerance, or food sensitivity, can happen when people have a difficult time digesting a certain food. Symptoms happen in the digestive system, not the immune system, and can be bloating, gas, and diarrhea. One common intolerance is lactose intolerance, when people can’t digest large amounts of lactose found in dairy products.