Sebaceous Cyst

The term "sebaceous cyst" is commonly used by the public to describe various skin cysts, but it is often not clinically accurate. The most common types of skin cysts often mistaken for sebaceous cysts are epidermoid cysts and pilar cysts. A true sebaceous cyst, known as a steatocystoma, is much rarer. Epidermoid Cysts are benign (non-cancerous) cysts that develop from the upper part of a hair follicle. They are lined by skin cells and filled with a thick, cheese-like, often foul-smelling substance called keratin. These cysts are also known as epidermal cysts, epidermal inclusion cysts, infundibular cysts, or keratin cysts. Pilar Cysts (also called trichilemmal cysts or wens) are benign cysts that originate from the outer root sheath of a hair follicle. They are lined by cells similar to those in the hair root and are filled with a smooth, dense keratin. Pilar cysts are most commonly found on the scalp. True Sebaceous Cysts (Steatocystoma) are rare cysts that arise from the duct of a sebaceous gland. They are lined by a thin layer of cells and contain an oily, yellowish, odorless fluid (sebum). These can appear as a single cyst (steatocystoma simplex) or multiple cysts (steatocystoma multiplex).

Symptoms

A small, round, firm, skin-colored or yellowish lump under the skin
Size varies from a few millimeters to several centimeters in diameter
Typically mobile under the skin
A small, dark, plugged opening (central punctum) may be visible on the surface of an epidermoid cyst
Epidermoid cysts commonly appear on the face, neck, chest, back, or scrotum
Pilar cysts occur on the scalp in over 90% of cases
May express a thick, white or yellow, cheese-like, foul-smelling material (keratin) if squeezed or ruptured
Usually painless if not inflamed or infected
Mild tenderness or discomfort without signs of infection (less common)
Calcification of the cyst wall, making it feel harder (less common)
Rapid increase in size (emergency symptom, may indicate infection or rarely malignancy)
Significant pain and tenderness (emergency symptom, may indicate infection)
Redness (erythema) and warmth of the overlying skin (emergency symptom, may indicate infection)
Purulent (pus) drainage (emergency symptom, may indicate infection)
Fever or chills (emergency symptom, systemic signs of infection)
Fixation to underlying structures (emergency symptom, very rarely suggests malignancy)
Ulceration or bleeding (emergency symptom, very rarely suggests malignancy)
Recurrence after complete excision (emergency symptom, very rarely suggests malignancy)

Causes & Risk Factors

Epidermoid cysts are caused by the proliferation of epidermal cells within the dermis, often due to a piece of epidermis becoming trapped in the skin after trauma or the occlusion of a hair follicle and its associated sebaceous gland.
Pilar cysts arise from the outer root sheath of the hair follicle, typically in the isthmus portion, and often have a strong genetic component with autosomal dominant inheritance.
True sebaceous cysts (steatocystoma) arise from the sebaceous gland duct.
The underlying mechanism for these cysts involves keratin-producing epithelial cells becoming trapped in the deeper layers of the skin, where they continue to produce keratin that accumulates and forms the cyst.
If the cyst wall ruptures, keratin is released into the surrounding skin, which can trigger a significant inflammatory response.
Age: Most common in adults, typically post-pubertal.
Gender: Epidermoid cysts are more common in men than women (approximately 2:1 ratio).
Skin Trauma: Injury to the skin, such as a surgical incision, abrasion, or acne, can increase the likelihood of epidermoid cyst formation.
Genetic Syndromes: Conditions like Gardner Syndrome (associated with multiple epidermoid cysts), Basal Cell Nevus Syndrome (Gorlin Syndrome), and Pachyonychia Congenita (associated with steatocystoma multiplex) can predispose individuals to these cysts.
Sun Exposure: Chronic sun exposure may be a contributing factor for epidermoid cysts on sun-exposed skin (possible factor).
Human Papillomavirus (HPV) Infection: Some evidence suggests a possible link, particularly for epidermoid cysts on the soles of the feet (possible factor).
Acne: Managing severe acne may reduce the formation of some epidermoid cysts (modifiable factor).
Skin Injury: Avoiding trauma to the skin may help prevent some cysts (modifiable factor).
Genetics: Hereditary predisposition, especially for pilar cysts (autosomal dominant inheritance) and syndromic cysts (non-modifiable factor).

Diagnosis

A healthcare professional will ask about the onset and duration of the lump, its growth rate, any history of trauma to the area, and if there is pain, redness, or drainage.
They will also inquire about personal or family history of similar cysts or relevant genetic syndromes (e.g., Gardner syndrome).
During a physical examination, the doctor will inspect the cyst for its size, shape, color, and the presence of a central punctum (a small, dark opening).
They will gently feel the cyst to assess its consistency (firm, soft, fluid-filled), how easily it moves under the skin, any tenderness, and if it is attached to deeper structures.
Diagnosis is primarily clinical, based on the characteristic appearance and feel of the lesion.
A definitive diagnosis is made by histopathological examination of the excised cyst under a microscope, especially if there is any suspicion of malignancy or if the diagnosis is uncertain.
For epidermoid cysts, histopathology shows a cyst lined by stratified squamous epithelium with a granular layer, filled with laminated keratin.
For pilar cysts, histopathology shows a cyst lined by stratified squamous epithelium without a granular layer, filled with dense, eosinophilic keratin.
Imaging is not typically required for uncomplicated cysts.
Ultrasound can be used to differentiate a cyst from a solid lump (like a lipoma) and to assess its size, depth, and relationship to surrounding structures.
MRI or CT scans are rarely used but may be considered for very large cysts or those in complex locations where underlying structures (nerves, vessels, bone) are a concern.
Other conditions that may look similar to a cyst include lipoma (a fatty lump, usually softer with no punctum), abscess (acutely painful, red, fluid-filled), dermatofibroma, pilomatricoma, neurofibroma, ganglion cyst (near joints), and very rarely, skin cancers like basal cell carcinoma or squamous cell carcinoma.

Treatment Options

For small, asymptomatic (not causing symptoms), and non-inflamed cysts, a healthcare professional may recommend watchful waiting, as cysts are benign and may remain stable for years without needing treatment.
Intralesional steroid injections can be used to reduce inflammation and size of an inflamed, non-infected cyst, but this is not a permanent cure and the cyst may return.
Oral antibiotics are prescribed for cysts that have become secondarily infected with bacteria (cellulitis); they treat the infection but do not remove the cyst itself.
Incision and drainage (I&D) is performed for acutely inflamed, tender, or abscessed cysts to provide immediate relief by draining the contents (keratin and pus). This procedure does not remove the cyst wall, so recurrence is common.
Surgical excision is the definitive treatment to prevent recurrence. It is performed on non-inflamed cysts for cosmetic reasons, recurrent inflammation, or when the diagnosis is uncertain.
During surgical excision, the entire cyst, including its wall (sac), is surgically removed under local anesthesia, and the skin is then closed with sutures.
Techniques for surgical excision include elliptical excision, minimal excision technique, or punch biopsy excision.
Emergency treatment involves incision and drainage for a painful, infected abscess, and systemic antibiotics may be required if there is surrounding cellulitis.
After surgical excision, follow-up typically involves suture removal 7-14 days later, depending on the location, and monitoring for signs of wound infection or cyst recurrence.
Referral to a dermatologist or surgeon is indicated for surgical excision, cysts in cosmetically sensitive or difficult locations (e.g., face, genitals), large or deep cysts, diagnostic uncertainty or suspicion of malignancy, or recurrent cysts.

Frequently Asked Questions

What is the difference between a sebaceous cyst, an epidermoid cyst, and a pilar cyst?

The term "sebaceous cyst" is often used generally, but it's usually a misnomer for epidermoid or pilar cysts. An epidermoid cyst forms from skin cells and is filled with a cheese-like keratin. A pilar cyst forms from hair follicle cells, often on the scalp, and contains dense keratin. A true sebaceous cyst (steatocystoma) is rare and originates from a sebaceous gland, containing oily fluid.

Is this lump cancerous?

Epidermoid and pilar cysts are almost always benign (non-cancerous). Malignant transformation into skin cancer is extremely rare, but it is more likely in older, larger, rapidly growing, or recurrent lesions. Your doctor will assess any suspicious changes.

Why does my cyst have a bad smell?

Epidermoid cysts are filled with laminated keratin, a cheese-like substance. If the cyst ruptures or is squeezed, this keratin can be released and often has a foul odor.

Do I need to have my cyst removed?

Not always. If a cyst is small, not causing any symptoms, and not inflamed, watchful waiting may be an option. Removal is typically recommended for cosmetic reasons, if it causes discomfort, becomes inflamed or infected, or if there's any diagnostic uncertainty.

What happens if I don't get it removed?

If left untreated, the cyst will likely persist and may slowly enlarge. There is an ongoing risk of it becoming inflamed, rupturing, or getting infected, which can cause pain and require medical attention.

Can I remove the cyst myself by squeezing it?

No, you should avoid squeezing or picking at a cyst. This can cause the cyst to rupture, leading to inflammation, infection, and potentially scarring. It also does not remove the cyst wall, meaning it will likely return.

What are the treatment options for my cyst?

Treatment options include watchful waiting for asymptomatic cysts, intralesional steroid injections to reduce inflammation, antibiotics for infected cysts, incision and drainage for acutely inflamed or abscessed cysts, and complete surgical excision for definitive removal and prevention of recurrence.

What is the difference between draining a cyst and surgically removing it?

Draining a cyst (incision and drainage) involves making a small cut to release the contents, providing immediate relief for an inflamed or infected cyst. However, the cyst wall remains, so the cyst is likely to return. Surgical removal (excision) involves removing the entire cyst, including its wall, which is the most effective way to prevent recurrence.

Will the cyst come back after treatment?

If a cyst is only drained (incision and drainage), there is a high chance it will recur because the cyst wall is left behind. If the entire cyst wall is completely removed during surgical excision, the recurrence rate is very low (less than 5%).

What does the surgical removal procedure involve?

Surgical removal is typically performed under local anesthesia. The surgeon makes an incision to carefully remove the entire cyst, including its sac. The skin is then closed with sutures. The procedure aims to remove the cyst completely to prevent it from returning.

Is the procedure painful?

During surgical removal, local anesthesia is used to numb the area, so you should not feel pain. You might feel some pressure or pulling. After the anesthesia wears off, you may experience some mild discomfort or soreness, which can usually be managed with over-the-counter pain relievers.

Will I have a scar after the cyst is removed?

Yes, some scarring is expected after surgical removal, as an incision is made. The size and appearance of the scar depend on the size and location of the cyst, the surgical technique used, and individual healing. Scarring can also occur after inflammation or rupture of a cyst.

What are the risks of surgical removal?

Potential risks of surgical removal include bleeding, hematoma (a collection of blood under the skin), wound infection, scarring, and very rarely, nerve damage depending on the cyst's location. Your doctor will discuss these risks with you.

How do I care for the wound after surgery?

After surgery, you will receive specific instructions for wound care. This typically involves keeping the area clean and dry, changing dressings as advised, and monitoring for signs of infection. Sutures are usually removed 7-14 days after the procedure, depending on the location.

When can I return to normal activities after the procedure?

Your doctor will provide specific guidance based on the cyst's location and your individual healing. Generally, you can return to most normal activities after the wound has healed and sutures are removed, typically within 7-14 days. Strenuous activities might need to be avoided for a bit longer.

Why did my cyst suddenly become red, swollen, and painful?

These symptoms often indicate that the cyst has become inflamed or infected. This can happen if the cyst wall ruptures, releasing its contents and causing a sterile inflammatory reaction, or if bacteria enter the cyst, leading to an infection or abscess formation.

Does an infected cyst need antibiotics?

Yes, if a cyst becomes secondarily infected with bacteria, oral antibiotics are typically prescribed to treat the infection. For an abscessed cyst, incision and drainage may also be necessary to release pus.

Can you remove a cyst while it is inflamed or infected?

Generally, complete surgical excision is best performed on non-inflamed cysts. If a cyst is acutely inflamed or infected, it is usually treated first with incision and drainage and/or antibiotics to resolve the infection. Definitive surgical removal may be planned once the inflammation has subsided.

Are these cysts hereditary?

Pilar cysts often have a strong genetic component and can run in families (autosomal dominant inheritance). Some epidermoid cysts can also be associated with rare genetic syndromes like Gardner Syndrome. However, many cysts occur without a clear hereditary link.

Can diet or lifestyle changes prevent these cysts from forming?

There is no strong evidence that specific diet or lifestyle changes can prevent these cysts from forming, especially those with a genetic predisposition. However, maintaining good skin hygiene and avoiding squeezing or picking at existing cysts can help prevent inflammation and infection.

Is it safe to remove a cyst during pregnancy?

Elective cyst removal is typically deferred until after delivery. However, if a cyst becomes acutely infected and requires incision and drainage, this can be performed safely during pregnancy using local anesthetics considered safe for pregnant women (e.g., lidocaine without epinephrine).

What is the black dot in the middle of my cyst?

A small, dark, plugged opening, often called a central punctum, can sometimes be seen on the surface of an epidermoid cyst. This is a characteristic feature and represents the opening of the hair follicle from which the cyst originated.

Does the location of the cyst (e.g., scalp vs. back) change the treatment?

While the general treatment options (watchful waiting, drainage, excision) apply regardless of location, cysts in cosmetically sensitive areas (like the face) or difficult locations may require a referral to a specialist for careful surgical planning to minimize scarring or address anatomical complexities.

When should I be concerned and see a doctor about my cyst?

You should see a doctor if your cyst rapidly increases in size, becomes significantly painful, red, or warm, starts draining pus, or if you develop a fever or chills. Also, seek medical advice if the cyst becomes fixed to underlying structures, bleeds, ulcerates, or recurs after complete removal, as these are very rare signs that could suggest malignancy.