Itchy papule: what causes it?

Both aesthetically and socially disturbing, papules can also be physically uncomfortable and itchy. Itchy papules have very specific causes, the most common of which are eczema, psoriasis and insect bites.

• Eczema can manifest as itchy papules.

  Whether genetic or acquired, eczema is a chronic inflammatory condition primarily due to a damaged skin barrier, making the skin drier and more permeable to irritants and allergens, and an exaggerated immune response. This latter is mainly due to the activation of T lymphocytes and the release of pro-inflammatory cytokines. These molecules promote the accumulation of immune cells in the affected area, leading to the formation of papules that are red and itchy. Eczema papules frequently develop on the face, elbows, knees, hands, and feet.

• Psoriasis can lead to the development of itchy papules.

  A chronic autoimmune disease, psoriasis manifests itself through the formation of thick, scaly patches, often accompanied by red papules that can itch. This skin condition is characterised by a failure of the immune system which abnormally produces inflammation molecules stimulating the proliferation of keratinocytes. This results in a thickening of the epidermis and the formation of papules. The inflammation found in psoriasis, mediated by T-lymphocytes, is macroscopically manifested as itching. The itchiness is also linked to the release of neuropeptides and chemical substances that stimulate the sensory nerves of the skin. Most often, psoriasis appears on the elbows, knees or scalp.

• Insect bites can cause itchy papules.

  Papular urticaria is a hypersensitivity reaction to insect bites, such as mosquitoes, fleas, or bedbugs. When an insect bites, it injects a small amount of saliva into the skin, which contains foreign proteins that trigger an immune response. Mast cells, which are connective tissue cells belonging to the immune system, release histamine. This causes a dilation of the blood vessels and a build-up of fluid in the surrounding tissues, leading to the elevation of the skin and the formation of red papules. Furthermore, histamine directly affects the nerve endings in the skin, resulting in intense itching.