International Business Department           Liu Bojia           January 05, 2023

  There are quite a number of people who have the habit of being picky eaters in their lives. Some may not be able to tolerate a particular characteristic of food, such as odour, appearance or taste, while others are passively picky because they are allergic to food. Taking seafood as an example, people with allergies may have allergic reactions such as itchy skin and diarrhoea after eating seafood, while under extreme conditions, a small number of people may feel dizzy and nauseous at the smell of seafood.

  With the popularity of modern city life, the incidence of allergies is on the rise. Biologically, allergies are essentially a type of inflammatory reaction, and whether it's sneezing, itchy skin or vomiting, allergies seem to be a means of defence for the body to expel toxic substances. Other studies have also speculated that our avoidance of certain foods is a symptom of allergies, as a way to reduce the harmful effects of foreign substances on the body.

  And when it comes to defences, we have to think of the immune system that has always helped us fight off foreign pathogens. According to past studies, histamine secreted by a type of immune cell called mast cells is key to the production of allergy symptoms. According to two studies in Nature, this response from mast cells can indeed be unpleasant, but it is actually reducing our chances of coming into contact with allergens and preventing the body from suffering damage.

  In one of the studies, from the German Cancer Research Centre, researchers first sensitised mice to ovalbumin by injecting the protein under the skin. The mice had access to two types of drinking water in their living environment, regular drinking water and water with ovalbumin added to it.

  The results showed that the untreated mice preferred the ovalbumin water, while the sensitised mice drank only regular water, and even when these mice "accidentally" drank the ovalbumin water, they would only taste it before stopping.

  The study found that the sensitised mice's avoidance of the protein water depended on two conditions: the presence of mast cells and IgE antibodies. Mice genetically engineered to lack mast cells or to produce IgE did not refuse to drink ovalbumin-containing water, even after they had completed the ovalbumin sensitisation immunisation process.

  However, just because the mouth of sensitised mice can accept it doesn't mean that their bodies can accept it as well. They will develop symptoms of gastritis and enteritis after drinking ovalbumin-containing water, which suggests that mast cells protect individuals from allergen damage.

  By coincidence, a team of researchers from Yale University also confirmed that mast cells prevent allergic mice from drinking ovalbumin water. In their study, they further found that when mice are exposed to allergens, the nucleus tractus solitarius and the central amygdala of the brain are activated, and these brain regions are responsible for producing an aversion response. The study confirmed that the mice's avoidance of the allergic food was also not possible without the involvement of these brain regions, which is not difficult to explain why we naturally develop an aversion to certain foods.

  In addition, leukotrienes, a biologically active molecule released by mast cells that have been identified to act as pro-inflammatory messengers to activate sensory nerves, also play a role in promoting avoidance behaviour. If mast cells were prevented from producing leukotrienes, sensitised mice also no longer avoided drinking ovalbumin water.

  The researchers point out that the human skin and gut are relatively more exposed to foreign substances, so they also have a more active immune response against non-infectious antigens, including allergy-causing foods. This response causes us to avoid further ingestion of allergens and stops inflammatory diseases from occurring, which is a natural protective measure.