What Is a Cyst?

Medically reviewed by Susan Bard, MD

A cyst is a pouch or sac-like pocket of tissue that may be filled with fluid, air, pus, or another material. These growths can form anywhere on or in your body and are usually not harmful. The majority of cysts occur in the skin, ovaries, breasts, or kidneys.

Many cysts don't cause any symptoms. If they do, the symptoms you experience would depend on where the cyst is located. For instance, a cyst affecting the skin might cause pain, redness, or discomfort. A cyst affecting the ovaries might cause pain and swelling. Most cysts won't require treatment and may even go away on their own. But if your cyst is causing you discomfort or poses a threat to your health, you may need some type of treatment. Treatments can range from drainage to surgical removal.

Types of Cysts

There are many types of cysts that can occur anywhere in your body. Some will appear under your skin and others will occur deep inside your body on your internal organs. Most of the time, cysts are harmless, but they can sometimes impact your health. Some cysts you can get include:

Baker Cyst

Also known as a popliteal cyst, a Baker cyst is one of the most common knee disorders. These fluid-filled sacs typically occur on the back of the knee and usually do not require treatment. Many times, they are caused by a knee injury such as a meniscus tear or osteoarthritis.

Bartholin Gland Cyst

This type of cyst is usually a blockage of one of the Bartholin glands, which are located at the vagina's opening. Typically, these cysts are found during a pelvic exam or imaging test. Bartholin gland cysts can occur for a number of reasons, including childbirth or trauma to the area.

Bone Cyst

This cyst occurs inside a growing bone and is typically found in the longer bones, like the legs and arms. Usually, bone cysts don't have any symptoms and go away on their own. But sometimes these cysts can increase the risk of fractures.

Breast Cyst

These non-cancerous (benign) cysts are one of the most common causes of breast lumps and develop in either one or both breasts. Often caused by normal fluctuations in hormones, these cysts can feel hard or soft to the touch and can sometimes feel uncomfortable or painful. Some people will not feel them at all.

Colloid Brain Cyst

This slow-growing, non-cancerous cyst is usually found near the center of your brain. If this cyst gets large enough, it can interrupt the flow of cerebrospinal fluid, causing hydrocephalus (a buildup of cerebrospinal fluid in the brain) and elevated pressure in your brain. People with these cysts may experience memory problems, headaches, confusion, and sometimes even loss of consciousness. Surgery is usually recommended when the cyst is large because it could be life-threatening.

Epidermoid Cyst

These cysts are the most common type of skin cysts and can occur anywhere on your body. They might also be referred to as epidermal inclusion cysts. Epidermoid cysts are under the surface of the skin and have a have a small, dark-colored opening. They can appear anywhere on your body, though the small lumps are most common on your face, neck, and torso. These cysts rarely cause problems or need treatment, though they can sometimes become painful.

Ganglion Cyst

These are the most common cause of masses or lumps in your hand. While they can occur anywhere on the hand, they usually develop on the back of your wrist. These non-cancerous fluid-filled sacs can appear quickly and disappear just as quickly. They usually produce no symptoms unless they are pressing on a nerve. In that case, you may feel some tingling sensations.

Hepatic Cyst

These cysts are fluid-filled cavities in your liver that usually don't cause any symptoms. They're typically found incidentally when you have an imaging study done. Most hepatic cysts are benign, but they can sometimes become cancerous or lead to complications like a hemorrhage or rupture. 

Ovarian Cyst

Ovarian cysts are fluid-filled sacs found in the ovary. They are common and form during ovulation. In some people, the ovaries make a lot of small cysts, which is called polycystic ovary syndrome (PCOS). It is rare that ovarian cysts become cancerous, but since it is possible, they should be checked for and monitored.

Simple Kidney Cyst

Simple kidney cysts can form in one or both of your kidneys and are fluid-filled sacs that can vary in size. Some are as small as a pea, and others can be as large as a golf ball. While simple kidney cysts are harmless, it is important to note that they are different from cysts found in polycystic kidney disease (PKD). PKD can cause chronic kidney disease while simple kidney cysts do not impact kidney function.

Benign vs. Malignant Cysts

Most of the time, cysts are benign, meaning they are not cancerous. Most cysts never even have the chance of becoming cancerous. However, some cysts might become cancerous, or malignant.

For instance, some ovarian cysts might become cancerous. This is truer for complex ovarian cysts, which are cysts that are solid. One example of a complex ovarian cyst is a dermoid cyst. Dermoid cysts are a common type of cyst for females aged 20-40 years. The cyst can contain solid material like teeth, hair, or fat. While it is possible for this type of ovarian cyst to be cancerous, it is still rare.

Why Does a Person Get Cysts?

There are different causes of cysts, depending on where in or on the body it forms. Sometimes the lumps can be caused by infections or injuries. Even parasites, like some types of roundworms and tapeworms, can cause cysts to form in your muscles, liver, brain, lungs, and eyes.

A meniscus tear could potentially cause a Baker cyst. Childbirth can cause a Bartholin gland cyst, while hormone fluctuations may cause a breast cyst. Hormone fluctuations can also cause some types of ovarian cysts, though ovarian cysts can develop for other reasons, including endometriosis. An epidermoid cyst under the skin may be caused by a blocked hair follicle.

Each type of cyst has a unique origin.

You might also be likelier to develop certain cysts based on factors like family history and age. For instance, people who get epidermoid cysts may have family members who also have them. You're also more likely to get these type of skin cysts as an adult.

Symptoms of Cysts

Some cysts may not cause any symptoms and will eventually go away on their own. For instance, liver and kidney cysts may not cause any symptoms at all.

Cysts can cause symptoms, though. Breast cysts may be painful. Baker cysts may cause pain and fullness behind the knee. Colloid brain cysts may cause confusion, headaches, and memory issues.

Most ovarian cysts are small and don't cause any symptoms. If ovarian cysts do cause symptoms, you may feel pressure, bloating, swelling, or pain on whichever side of the lower abdomen the cyst is.

The only symptom of an epidermoid cyst is usually just the lump itself. There will probably be a tiny hole in the center of the lump.

Ultimately, your symptoms will depend largely on the type of cyst you have and where it is located. Factors like the cyst's size and whether it ruptures or becomes infected can also impact what types of symptoms you experience.

How Do You Remove a Cyst?

Whether a cyst even needs to be removed is something you and your healthcare provider can discuss. Since most cysts are harmless, they might not need to be removed. Instead, many cysts will resolve on their own or with simple at-home treatment. For instance, placing a warm, damp cloth on an epidermoid cyst can help it drain and go away.

If it's determined that a cyst should be removed, the removal process is different depending on which type of cyst you have. Sometimes cysts can be removed in a practitioner's office. Other times, surgery will need to be scheduled. There also are times when cysts can be drained or treated with medications to reduce their size.

If you have a cyst that you can visibly see on your body, don't try to remove it yourself.

What Can Happen if a Cyst Is Left Untreated?

Depending on the type, location, and effect of the cyst, it may be OK to leave a cyst untreated since many don't cause harm and can go away on their own.

Other times, not treating a cyst can cause complications. This might include infection or rupture, where the cyst breaks open. If a cyst is not completely removed with surgery, it can come back. In the cases of malignant cysts, not treating them can mean the potential for the cancer to spread.

When to See a Healthcare Provider

When a cyst is in or on an internal organ, you might not know you have it until you're getting examined for an unrelated reason or as part of a routine exam. If a healthcare provider tells you you have a cyst, there are some signs or symptoms that should warrant a talk with a healthcare provider.

If you know you have an ovarian cyst and experience sudden, severe abdominal pain or heavy bleeding, you should contact a healthcare provider. These might be signs that the cyst has ruptured. Other signs of a ruptured ovarian cyst include fever, vomiting, and dizziness.

In the case of cysts that affect your skin, you can more easily see for yourself that you may have a cyst. Anytime you have a new lump or bump, consider seeing a healthcare provider for an accurate diagnosis. If it's confirmed that you have a cyst of the skin and the cyst becomes inflamed, swollen, tender, large, or infected, you should see a healthcare provider. They may need to provide special treatment.

A Quick Review

A cyst is a pocket of tissue that is full of fluid, air, pus, or other substance. The growths can occur anywhere in your body and are usually benign, or non-cancerous. There are many types of cysts. Common cysts include breast cysts, ovarian cysts, epidermal inclusion cysts, and ganglion cysts. Cysts might not cause any symptoms and also may not require treatment. However, if your cyst is causing you pain or discomfort or interfering with your life in some way, it may be helpful to ask a healthcare provider for advice on how to treat it.

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