From MedlinePlus Genetics
Dowling-Degos disease is a skin condition characterized by a lacy or net-like (reticulate) pattern of abnormally dark skin coloring (hyperpigmentation), particularly in the body's folds and creases. These skin changes typically first appear in the armpits and groin area and can later spread to other skin folds such as the crook of the elbow, back of the knee, and under the breasts. Less commonly, pigmentation changes can also occur on the neck, wrists, back of the hands, face, scalp, scrotum, and vulva. These areas of hyperpigmentation typically cause no health problems.

Individuals with Dowling-Degos disease may also have dark spots (lesions) on the face and back that resemble blackheads, red bumps around the mouth that resemble acne, or pitted scars on the face similar to acne scars but with no history of acne. Fluid-filled sacs within the hair follicle (pilar cysts) may develop, most commonly on the scalp. Rarely, affected individuals have patches of skin that are unusually light in color (hypopigmented).

A condition called Galli-Galli disease has signs and symptoms similar to those of Dowling-Degos disease. In addition to pigmentation changes, individuals with Galli-Galli disease also have a breakdown of cells in the outer layer of skin (acantholysis). Acantholysis can cause skin irritation and itchiness and lead to reddened or missing patches of skin (erosions). These conditions used to be considered two separate disorders, but Galli-Galli disease and Dowling-Degos disease are now regarded as the same condition.

In rare cases, individuals with Dowling-Degos disease experience itching (pruritus) or burning sensations on the skin. These feelings can be triggered by UV light, sweating, or friction on the skin.

The pigmentation changes characteristic of Dowling-Degos disease typically begin in late childhood or in adolescence, although in some individuals, features of the condition do not appear until adulthood. New areas of hyperpigmentation tend to develop over time, and the other skin lesions tend to increase in number as well. While the skin changes associated with Dowling-Degos disease may cause distress or anxiety, they typically cause no other health problems.  https://medlineplus.gov/genetics/condition/dowling-degos-disease