Itchy Papule: What Causes It?

Both aesthetically and socially disturbing, papules can also be physically bothersome 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, which makes 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 is characterized by the formation of thick, scaly patches, often accompanied by red papules that can itch. This skin condition is characterized by a failure of the immune system which abnormally produces inflammation molecules that stimulate the proliferation of keratinocytes. This leads to a thickening of the epidermis and the formation of papules. The inflammation found in psoriasis, mediated by T-lymphocytes, is manifested at the macroscopic level by itching. The itch is also related 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 buildup 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.