Why do certain food allergies cause spots?

Increasingly common, food allergies affect not only the gastrointestinal and respiratory tracts but also the skin, and can cause spots. As a reminder, a food allergy is defined as an immune response to a dietary protein. Thus, when a sensitive individual ingests an allergenic food, such as eggs, peanuts or shellfish, their immune system identifies certain proteins as intruders to be eliminated. There are two main types of food allergic reactions, both of which can cause spots:

• Food allergies mediated by Immunoglobulin E antibodies.

  This type of food reaction is the most common and occurs in two stages. During the first exposure to the food allergen, specific IgE antibodies are produced and attach to mast cells and basophils, which are immune cells. If a new encounter with the same allergen occurs, it is recognised by the IgE present on the cells, thus triggering their degranulation. This release leads to an influx of inflammatory mediators, including histamine, which plays a key role in the dilation of blood vessels and the onset of itching. The clustering of immune cells in the skin tissues also causes their swelling, visible in the form of small papules grouping into red patches: the allergy spots.

• Non-immunoglobulin E antibody mediated food allergic reactions.

  Also known as cell-mediated food allergies, non-IgE-mediated reactions involve T lymphocytes, specialized immune cells. When they encounter allergenic proteins, they release pro-inflammatory cytokines, molecules that attract other immune cells and amplify the inflammatory response. This process causes erythematous eruptions that resemble eczema eczema. These rashes are often located in the folds of the elbows and knees. Unlike those characteristic of urticaria, they tend to persist longer and are generally associated with more pronounced irritation.