What Is a Cyst?

A cyst is an abnormal sac-like growth or mass that looks like a pouch or capsule. Cysts can be filled with air, fluid, pus, or tissue. They can form just about anywhere in the body. Cysts are different from tumors, and are almost always benign (not cancer.)

What causes a cyst?

A cyst develops when a structure in the body gets blocked, such as a duct that carries or drains fluids. The blockage can be caused by an infection or another problem in the duct or nearby tissue or organ. The blockage can cause air, fluid, blood, or pus to build up, leading to a sac forming around the buildup. The sac and its contents make up what is called a cyst.

Types of cysts

Examples of common cysts include:

• Cysts found under the skin, such as ganglion, sebaceous, pilonidal, and dermoid cysts
• Fibrous and simple breast cysts
• Follicular and dermoid ovarian cysts and polycystic ovaries
• Simple renal (kidney) cysts and polycystic kidney disease

Symptoms of cysts

Cysts can have many different sizes and shapes. Some cysts can be felt with your hand, but some are deeper inside the body and can only be seen with x-rays or other imaging tests. If a cyst is in a spot where you can see and feel it, it may be soft or pliable to the touch if it contains air or fluid. But if it is filled with tissue, it can feel more firm and solid. 

Is a cyst cancer?

Almost all cysts are benign (not cancer). This means they do not have cancer cells inside them. While cysts have some cells, they are not usually filled with abnormal cells like cancerous neoplasms or tumors are. However, some cysts may contain cells that show signs of abnormal changes, and it’s possible they can turn into cancer.

Cyst versus tumor or neoplasm

A cyst is different from a neoplasm or tumor. Here are the key differences:

• Most cysts are benign. Tumors and neoplasms can be benign or malignant.
• Cysts are sacs or pouches filled with air, fluid, pus, or tissue. Tumors and neoplasms are made up of abnormal cells.
• Cysts form due to a blockage or infection in the body. Tumors and neoplasms form when something happens during the cell cycle process that results in abnormal cells forming, growing, and developing into a lump or mass.

Does a cyst need to be removed?

Some cysts might be removed due to size, location, or other concerns, while others can be left alone. If the cyst has fluid or pus that can be drained out, the cyst might go away after it’s drained. Sometimes it can refill with fluid or pus, or another cyst might form in the same area. 

While most cysts are harmless, any cyst that changes in size or shape, or causes symptoms, should be checked by a doctor. They can help you understand what might have caused a cyst to form and decide if it should be removed or not.