The exact cause of pityriasis rotunda is unknown, but some researchers believe that it may be a variant of ichthyosis vulgaris. Other researchers believe that pityriasis rotunda is caused by malnutrition, but this is not universally accepted. The presence of systemic disease, which is characteristic of type 1 pityriasis rotunda, appears to be most common in South African and Japanese individuals, but is less common among Caucasians. Type 1 most often occurs with stomach cancer and liver cancer. Other conditions that type 1 pityriasis rotunda has been associated with include:

• Other malignancies (chronic myeloid leukemia, squamous cell carcinoma, multiple myeloma)
• Liver disease
• Tuberculosis
• Heart disease
• Lung disease
• Chronic kidney disease
• Malnutrition
• Chronic diarhhea
• Scleroderma

It has been proposed that type 2 pityriasis rotunda, which is typically inherited in families and seen in lighter skinned individuals, is inherited in an autosomal dominant manner.

The lesions that result from pityriasis rotunda usually do not cause specific symptoms and/or lead to serious complications. However, pityriasis rotunda can occur with serious underlying systemic diseases and cancers, such as stomach cancer and liver cancer.Affected individuals usually have several lesions, ranging from 4 to 80, that are commonly found on the buttocks, thighs, abdomen, trunk, and upper and lower extremities. The patches are often almost perfectly circular and sharply defined with dry ichthyosis-like scaling. The lesions range between 0.5 and 20 cm in diameter and are generally isolated, although merging of lesions can create a polycylic shape. Colors range from pink to light-brown. Once the lesions develop, they usually remain unchanged throughout life unless the underlying internal disease or malignancy is treated, in which case, they resolve or improve.

There appear to be two types of pityriasis rotunda. Type 1 pityriasis rotunda usually affects South African and East/Southeast Asian individuals older than 60 years who tend to have associated malignancies (cancers) or systemic disease. The lesions found in those with type 1 are usually darker (hyperpigmented) than the surrounding skin; and other family members are not affected. Type 2 affects people with lighter skin who are younger than 40 years. These individuals do not have any associated malignancy or systemic diseases, but have multiple lesions that are lighter (hypopigmented) than the surrounding skin. Type 2 also tends to run in families.