Cysts

A cyst is a closed sac under the skin that contains fluid, semi-solid material, or keratin, which is a protein normally found in skin, hair, and nails. Most skin cysts feel like a small, round lump and may move slightly when touched. They can vary in size, from a pea to several centimeters across.

The most common type seen in dermatology offices is an epidermal inclusion cyst. These form just beneath the surface of the skin and are often filled with a thick, cheese-like material made of keratin. They are sometimes mistakenly called “sebaceous cysts,” although true sebaceous cysts are less common.

Cysts can develop almost anywhere on the body but are frequently found on the face, neck, chest, back, and scalp. In many cases, they grow slowly and do not cause pain. However, if a cyst becomes inflamed or infected, it can become red, swollen, tender, and sometimes drain.

Cysts form when skin cells move deeper into the skin instead of shedding off the surface. Normally, skin cells rise to the top layer and flake away. When these cells become trapped beneath the surface, they can multiply and form the wall of a cyst. The cells continue producing keratin, which builds up inside the sac and causes the cyst to enlarge.

Several factors may contribute to cyst formation. Blocked hair follicles are a common cause. When a pore becomes clogged due to oil, dead skin cells, or debris, it can lead to a cyst. Acne-prone skin is more likely to develop certain types of cysts because of frequent inflammation and clogged pores.

Genetics can play a role as well. Certain inherited conditions are associated with multiple cysts. In these cases, patients may notice recurrent or numerous cysts over time.

Most cysts appear as smooth, round bumps under the skin. They may have a small visible opening, sometimes called a punctum, in the center. The overlying skin is usually normal in color unless the cyst becomes inflamed.

A non-inflamed cyst is often painless. Patients may seek evaluation because of cosmetic concerns or because the cyst has gradually increased in size. Some cysts remain stable for years, while others enlarge slowly.

If a cyst becomes irritated or infected, symptoms can change. The area may become red, warm, swollen, and tender. In some cases, it may rupture and release its contents, leading to inflammation and discomfort. An infected cyst can resemble a boil and may require treatment to control pain and swelling.

Any rapid change in size, unusual firmness, persistent pain, or drainage should be evaluated by a dermatologist. Although most cysts are benign, not every lump under the skin is a cyst, and careful assessment is important.

Diagnosis typically begins with a thorough skin examination. Dr. Patricia Richey evaluates the size, shape, location, and texture of the lump. The feel of the growth, whether it moves under the skin, and whether there is a central opening all provide clues.

In most cases, cysts can be diagnosed based on a physical exam alone. Dermatologists are trained to recognize common skin growths and distinguish cysts from other conditions such as lipomas, abscesses, or skin cancers.

If there is uncertainty about the diagnosis, or if the growth has unusual features, a biopsy may be recommended. A biopsy involves removing part or all of the lesion and examining it under a microscope. This step ensures an accurate diagnosis and rules out more serious conditions.

When a cyst is removed, the tissue is often sent to a laboratory for confirmation. This is especially important if the cyst has atypical characteristics or if the patient has a history of skin cancer.

In rare situations, imaging studies such as ultrasound may be used to evaluate deeper or unusually large growths. However, most skin cysts do not require imaging.

Patients should consider evaluation if a lump under the skin continues to grow, becomes painful, changes in appearance, or interferes with daily activities. Even when a cyst is not bothersome, some individuals choose removal for cosmetic reasons or to prevent future inflammation. Attempting to squeeze or pop a cyst at home is not recommended. Doing so can cause inflammation, infection, and scarring.