Food allergies occur when the immune system – the body's defence against infection – mistakenly treats proteins found in food as a threat.
Symptoms range from skin redness, hives and swelling to - in the most severe cases - vomiting, diarrhoea, difficulty breathing and anaphylaxis which can lead to death.
Almost any food can cause an adverse reaction, such as wheat, gluten, egg, milk and tree nuts which led to the death of Karanbir Cheema, who died from an allergic reaction after pupils threw cheese at him.
There are 14 ingredients that have been identified as causing most food allergies.
So what are these ingredients, what symptoms do they cause and what does the law state when it comes to listing them?
The 14 ingredients known to cause most allergies
Celery - including any found in stock cubes and soup
Cereals containing gluten - including spelt, wheat, rye, barley
Crustaceans - eg crabs, lobster, prawns and shrimp paste
Eggs - including food glazed with egg - this can include baked goods such as cakes, biscuits and pies
Fish - often found in fish sauces, pizzas, relishes, salad dressings,stock cubes and Worcestershire sauce
Lupin - can be found in some types of bread, pastries, pasta
Milk - is a common ingredient in butter, cheese, cream, milk powders and yoghurt
Molluscs - mussels, land snails, squid, also found in oyster sauce
Nuts - for example almonds, hazelnuts, walnuts, macadamia
Peanuts - also found in groundnut oil
Sesame seeds - found in some bread, houmous, tahini
Soya - found in beancurd, edamame beans, tofu
Sulphur dioxide - used as a preservative in dried fruit, meat products, soft drinks, vegetables, alcohol.
Symptoms of an allergic reaction
Symptoms can develop within a few minutes or even over a few hours of being exposed to an allergen.
Common symptoms of an allergic reaction, according to the NHS, include sneezing, an itchy or running nose, itchy or red watering eyes, itchy or patchy skin, wheezing, chest tightness, shortness of breath as well as stomach pain, feeling sick, vomiting and diarrhoea.
In rare cases an allergy can lead to a severe allergic reaction, called anaphylactic shock, which can be life threatening.
This affects the whole body and usually develops within minutes of exposure to something you're allergic to.
What does the law state when it comes to labelling of foods that cause allergies?
In 2014, EU legislation came into force (under FIC Food Information for Consumers Regulation) which required restaurants, takeaways, bakeries, and cafes to tell customers if their food contained the 14 ingredients listed above.
Supermarkets or stores selling pre-packaged products were also required to comply with the law change.
However, in the UK freshly handmade, non pre-packaged food, did not have to be individually labelled.
In May 2019, the Food Standards Agency urged for tougher legislation.
It said retailers that prepare and package food to sell on-site should list all ingredients they use to avoid allergy deaths.
The FSA advised ministers that food outlets should place labels on products, which include a full list of ingredients with all 14 major allergens highlighted.
Currently, food prepared and sold on-site does not require warning labels about potential allergens because it is assumed that customers who require information will question staff.
The changes were proposed following the death of Natasha Ednan-Laperouse, who died after eating a sandwich from Pret A Manger which contained sesame.
The teenager had an allergy to sesame which was not listed on the baguette she bought.
And it's now been announced by Environment Secretary Michael Gove that a new law reflecting these changes will come into force in England and Northern Ireland in summer 2021.