GWENT trading standards officers launched a food safety crackdown after discovering take-aways and restaurants across the region were risking peoples' lives.
Undercover officers visited 36 establishments in Blaenau Gwent, Caerphilly, Newport and Torfaen.
After conducting analysis, they discovered three of the meals purchased contained peanut protein, despite officers specifically requesting peanut-free food.
A spokesman for Torfaen council trading standards said one in seven people in the UK suffers from allergic reactions caused by food, which can lead to a life-threatening condition known as anaphylaxis. The sufferer experiences a rapid drop in blood pressure and loss of consciousness.
He said: "The most common foods to cause life-threatening reactions include peanuts and tree nuts, such as walnuts, almonds, Brazil nuts, hazelnuts and pistachios.
"People tend to dine out more and rely on others to prepare the food they consume. That's where peanut allergy sufferers are most at risk. Most deaths have occured where people have eaten out."
Trading standards have confirmed they have sent out warnings and will be "taking steps" to bring the problem to the notice of chefs and cooks in take-aways in Gwent.
Less serious food allergy symptoms include rashes, swelling of the lips and face, vomiting or difficulty breathing.
Despite legislation requiring pre-packed food to list any allergens they contain, restaurants and take-aways are not required by law to label food, leaving diners at the mercy of chefs.
But it is a criminal offence under the Food Safety Act 1990, or Trade Descriptions Act 1968, to supply food which is not as described or demanded.
Hazel Gowland, food adviser to the Anaphylaxis Campaign said: "Projects such as these, undertaken by trading standards, are key to understanding where exactly food may carry hidden risks.
"The number of people with food allergies is on the increase. For some it's a matter of life or death.
"It is vital food businesses know exactly what is in the food they sell and understand how to prevent cross-contamination from allergens, particularly nuts and peanuts."
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