Skin allergies: what are the causes of itching?

Unpleasant but quite common, skin allergies occur when the body overreacts to a substance it mistakenly perceives as a threat. These are referred to as allergens. They can be chemicals, cosmetics, foods, medicines or even materials, such as latex. In response to allergens, mast cells and basophils, cells of the immune system, release histamine, a molecule involved in redness, swelling but also the itching characteristic of a skin allergy. There are several types of skin allergies, the main ones being contact eczema and urticaria.

Also known as contact dermatitis, contact eczema is the result of a delayed hypersensitivity. The first time the allergen comes into contact with the skin, antigen-presenting cells, such as Langerhans cells, capture the allergen and present it to T lymphocytes. These become sensitised and, upon subsequent exposure, trigger the release of pro-inflammatory mediators such as interleukins, which intensify the inflammation and itching caused by histamine. As for urticaria, it is an immediate skin reaction resulting from the rapid degranulation of mast cells and the massive release of histamine and pro-inflammatory cytokines.

When histamine binds to H1 receptors located on the terminals of C fibres, specialised nerve fibres, it triggers the release of certain neurotransmitters and initiates the transmission of itch signals to the central nervous system via the spinal cord. Other receptors, also located on the C fibres, can intensify the itch: the TRPV1 receptors, which are also sensitive to heat, and TRPA1, which also play a role in sensations of pain and cold. Other types of nerve fibres, such as A-delta fibres, although primarily involved in pain transmission, can sometimes be stimulated in cases of itching.

How to alleviate itching caused by a skin allergy?

In addition to medications and balms prescribed by the doctor, there are certain tips that can help to alleviate the itching experienced following a skin allergy. A simple but effective method is to apply cold to the itchy area. Indeed, thanks to its vasoconstrictive properties, the cold can reduce blood flow and thus limit the circulation of inflammatory mediators responsible for itching. If you use ice cubes, be sure not to apply them directly to your skin but to wrap them in a clean cloth, to avoid burning yourself. You can also use certain soothing essential oils, such as true lavender essential oil or ginger essential oil, provided you dilute them first in a vegetable oil.