Darier's disease (DAR) is a rare, inherited skin disorder that presents with multiple greasy, crusting, thick brown bumps that merge into patches. It is an autosomal dominant disorder discovered by French dermatologist Ferdinand-Jean Darier. Mild forms of the disease are the most common, consisting solely of skin rashes that flare up under certain conditions such as high humidity, high stress, or tight-fitting clothes. Short stature, when combined with poorly-formed fingernails that contain vertical striations, is diagnostic even for mild forms of DAR. Symptoms will usually appear in late childhood or early adulthood between the ages of 15 and 30 years and will vary over the lifespan. More severe cases are characterized by dark crusty patches on the skin that are mildly greasy and that emit a strong odor. These patches, also known as keratotic papules, keratosis follicularis, or dyskeratosis follicularis, most often appear on the scalp, forehead, upper arms, chest, back, knees, elbows, and behind the ear.

Reference
Wiki: Keratosis follicularis