Causes of back cysts include sun exposure, acne, trauma, developmental defects and hereditary diseases, such as Gardner’s syndrome and basal cell nevus syndrome, according to Healthline. Sebaceous cysts and epidermoid cysts are two types of cysts that appear on the back, and each have distinct causes.
Sebaceous cysts form when the oil that coats the skin gets trapped due to a damaged or blocked sebaceous gland, notes Healthline. The most common cause of a sebaceous cyst is trauma to the area, which may be due to acne, scratching or surgery. Because sebaceous cysts develop slowly over time, the trauma often occurs a long time before the cyst becomes noticeable. People who are born with a deformed sebaceous gland duct also experience sebaceous cysts.
Epidermoid cysts appear as small, hard lumps beneath the skin, explains Healthline. These cysts are typically caused by a buildup of keratin beneath the skin. Keratin buildup is caused by damage to the skin or hair follicles, which has various causes, including sun exposure, acne and skin conditions.
Gardner’s syndrome can cause both sebaceous and epidermoid cysts, according to Cancer.net. Patients with this disorder also experience fibromas, desmoid tumors and osteomas, which are all noncancerous growths that develop in different organs. The condition is diagnosed through a blood test, and patients with Gardner's syndrome have a higher risk of developing cancer.