A lipoma is a benign tumor made of fat tissue. They are generally soft to the touch, movable, and painless. They usually occur just under the skin, but occasionally may be deeper. Most are less than 5 cm (2.0 in) in size. Common locations include upper back, shoulders, and abdomen. It is possible to have a number of lipomas.The cause is generally unclear. Risk factors include family history, obesity, and lack of exercise. Diagnosis is typically based on a physical exam. Occasionally medical imaging or tissue biopsy is used to confirm the diagnosis.Treatment is typically by observation or surgical removal. Rarely, the condition may recur following removal, but this can generally be managed with repeat surgery. They are not generally associated with a future risk of cancer.Lipomas have a prevalence of roughly 2 out of every 100 people. Lipomas typically occur in adults between 40 and 60 years of age. Males are more often affected than females. They are the most common noncancerous soft-tissue tumor. The first use of the term "lipoma" to describe these tumors was in 1709. Types
The many subtypes of lipomas include:: 624–5 
Adenolipomas are lipomas associated with eccrine sweat glands. : 627 
Angiolipoleiomyomas are acquired, solitary, asymptomatic acral nodules, characterized histologically by well-circumscribed subcutaneous tumors composed of smooth muscle cells, blood vessels, connective tissue, and fat. : 627 
Angiolipomas are painful subcutaneous nodules having all other features of a typical lipoma. : 624 
Cerebellar pontine angle and internal auditory canal lipomas
Chondroid lipomas are deep-seated, firm, yellow tumors that characteristically occur on the legs of women.
Lipomas growing in internal organs can be more dangerous; for example, lipomas in the gastrointestinal tract can cause bleeding, ulceration, and painful obstructions (so-called "malignant by location", despite being a benign growth histologically). Malignant transformation of lipomas into liposarcomas is very rare, and most liposarcomas are not produced from pre-existing benign lesions. A few cases of malignant transformation have been described for bone and kidney lipomas, but it is possible that these few reported cases were well-differentiated liposarcomas in which the subtle malignant characteristics were missed when the tumor was first examined. Deep lipomas have a greater tendency to recur than superficial lipomas because complete surgical removal of deep lipomas is not always possible.The presence of multiple lipomas, lipomatosis, is more commonly encountered in men. Some superficial lipomas can extend into deep fascia and may complicate excision. Liposarcoma is found in 1% of lipomas and is more likely to occur in lesions of the lower extremities, shoulders, and retroperitoneal areas. Other risk factors for liposarcoma include large size (>5 cm), associated with  calcification, rapid growth, and/or invasion into nearby structures or through fascia into muscle tissue. Epidemiology
Around 2% of the general population has a lipoma. These tumors can occur at any age, but are most common in middle age, often appearing in people from 40 to 60 years old.