Postinflammatory Hyperpigmentation in the Epidermis
According to Dr. Schwartz at the UMDNJ-New Jersey Medical School, one of the most common ways for scratching to lead to hyperpigmentation is postinflammatory hyperpigmentation (PIH). The epidermis, the top layer of the skin, can become inflamed as a result of mild skin trauma, such as scratching. Once the skin becomes inflamed, the immune response causes a number of chemical signals to be released, which include prostaglandins, leukotrienes and other products (these are all chemicals involved in the immune system). When these immunological signals are released, they activate the melanocytes and cause them to release melanin. Melanin is the primary pigment that is responsible for skin color. The inflammation of the epidermis that occurs as a result of scratching results in excessive melanin release, leading to hyperpigmentation of the skin.
Postinflammatory Hyperpigmentation in the Dermis
The dermis is the layer of skin under the epidermis, which can also be affected by PIH, but from a different mechanism. Excessive scratching of the skin can cause damage to the cells of the dermis directly and may result in the basal cells (those responsible for making new skin cells) to be disrupted. When this occurs, melanin is released from the basal cells and is absorbed by a type of immune cell called a macrophage. As a result, the macrophage cells in the dermis become pigmented, which leads to dermal hyperpigmentation. This type of hyperpigmentation occurs as a result of heavier trauma.
Eczema and Hyperpigmentation
Eczema occurs when the immune system becomes hyperreactive, leading to chronic inflammation and redness. One of the symptoms of chronic eczema is dryness and itchiness of the skin, which can lead to persistent scratching. Eczema patients who scratch the affected areas are especially prone to PIH because the skin cells are already inflamed, making them sensitive to additional irritation. Many people with eczema also suffer from hyperpigmentation aside from scratching, as the chronic inflammation of their skin cells is sufficient to cause hyperpigmentation in and of itself.
