Cells constantly grow, die, and are replaced by new cells. When this process fails, excess cell growth can lead to tumors. Benign tumors are non-cancerous and cannot invade other tissues, but because they can form anywhere, they often scare people. They are quite common: nine out of ten women experience a benign breast mass in their lives. Benign bone tumors are also significantly more common than their malignant counterparts.

Adenoma

A tumor growth on the thin layer of glandular tissue that covers organs such as the stomach, colon, and small intestine is an adenoma. Though benign, adenomas can become malignant in rare situations. Even when benign, however, adenomas can cause serious issues by pressing on other tissues and causing excess hormone secretions. Occasionally, the growths are too small to see macroscopically but still large enough to cause physiological problems. Adenomas grow at different rates based on their location, which enables doctors to easily predict growth.

Lipoma

Soft to the touch and easy to move, lipomas are benign tumors composed of fat tissue. There are a large number of lipoma subtypes. Adenolipomas develop in the eccrine sweat glands. Hibernomas are tumors that develop from the brown fat found most commonly in newborns and hibernating mammals. The most common type of lipoma is the superficial subcutaneous lipoma. These are usually under five centimeters in size and occur just under the skin. People usually develop these lipomas in their upper back, abdomen, and shoulders.

Myoma

Benign tumors can also grow in the muscles. Myomas grow from the blood cells or the muscles and have many subtypes. If the growth is in smooth muscle such as the stomach or uterus, it is a leiomyoma. Striated muscle tumors are rhabdomyomas; they occur in the heart, tongue, and vagina. Leiomyomas are the most common benign esophagus tumors, and cardiac rhabdomyomas are the most common primary heart tumor in children. Though myomas can become cancerous, this is rare.

Nevus

Better known as moles, beauty marks, and birthmarks, nevi have a variety of causes and classifications. A nevus can be congenital or develop from issues later in life. Many disorders or complications involving the pigmenting agent melanin cause nevi. These melanocytic tumors are typically benign but can result from cancerous growths. A nevus is not always an external, dark growth. In some cases, they appear as a white patch due to a lack of melanin.

Fibroma

When fibrous or connective tissue grows a tumor, it is called a fibroma. Doctors consider many other types of benign tumors, such as several myomas, subcategories of fibroma. These tumors grow in any organ and anywhere on the skin. Scars, skin tags, and ovarian growths are fibromas. Keloid scars are the most tumor-like. The ovaries produce estrogen and progesterone which allow the uterine lining to regrow, but also stimulate the growth of fibromas. Most fibromas are asymptomatic, though ovarian fibromas can cause abdominal pain.

Polyps

The mucous membranes can develop fleshy growths called polyps. Polyps in the colon or rectum are colorectal polyps. Those that develop in the upper part of the stomach are fundic gland polyps. These are the most prominent types of polyp but can develop anywhere there is a mucous membrane. Like nevi, polyps are usually benign, though they can be the result of cancerous growths. Some polyps can cause bleeding and in rare cases lead to intense abdominal pain.

Chondroma

Though rare, cartilage is not immune to the development of tumors. Doctors place these chondromas in one of two categories. An enchondroma grows within the bone and expands it outward, while a chondroma grows on the exterior of the bone and is much rarer. Doctors prefer to leave these tumors alone unless fractures are a concern. If that is the case, surgeons may opt to scrape the tumor away using a curette. If the affected person feels the tumor is unsightly or negatively affects their lives, they can request the surgery, as well.

Papilloma

Epithelial layers of tissue, such as the outer layer of the skin, develop tumors as well. Papillomas come in many varieties and categories and usually form cauliflower-shaped projections. They are often small, usually under five centimeters in size. The most common forms of papilloma are warts. Papillomas may also appear in the lips, tongue, cervix, vagina, or anal canal. These growths are often the result of human papillomavirus, though there are other causes about which little is known. There is no evidence papilloma tumors are premalignant.

Astrocytoma

Star-shaped brain cells called astrocytes can experience abnormal cell growth and develop astrocytomas. These tumors can develop anywhere in the brain and even occasionally grow in the spinal cord. A grading scale of I to IV defines the severity of the astrocytoma and its likelihood of becoming malignant. Stage I tumors are minor enough that doctors can remove them with surgery or treat them with radiation. However, beginning at stage II, the tumors are likely to reduce the lifespan of the affected person, even with treatment.

Osteoma

Bones and their surrounding tissue can develop tumors that are pieces of new bones. Osteomas commonly develop on the skull and have no known cause. Osteomas that grow from another bone are homoplastic. Those that grow on the surrounding tissue are heteroplastic. Because osteomas often grow on the skull, they can cause pain, headaches, and even sinus infections. The tumors can also press on the cranial nerves, causing palsies and loss of hearing or vision.