Skin Allergies: What are the causes of itching?

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

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 cells become sensitized 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.

The histamine then binds to H1 receptors located on the terminals of C fibers, specialized nerve fibers, which 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 fibers, 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 fibers, such as A-delta fibers, 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 a doctor, there are certain tricks that can help alleviate the itching experienced following a skin allergy. A simple but effective method is to apply cold to the itchy area. Indeed, due to its vasoconstrictive properties, 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, so as not to burn 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.