An epidermoid or epidermal inclusion cyst is a lump formed under the skin. This lump is filled with keratin flakes or debris. The term “sebaceous cyst” is a common misnomer used for epidermoid cysts. These cysts are usually harmless and do not require removal unless they cause symptoms or for cosmetic reasons.
What is an epidermoid cyst?
An epidermoid cyst is a benign (non-cancerous) skin growth filled with keratin, the protein found in the outer layer of the skin.
These cysts are also known by other names, including epidermal cysts, epidermal inclusion cysts (EIC), keratin cysts, follicular infundibular cysts, or simply infundibular cysts.
Epidermoid cyst vs. sebaceous cyst
The terms “epidermoid cyst” and “sebaceous cyst” are often used interchangeably, but they are not the same.
In most cases, what is referred to as a sebaceous cyst is, in fact, an epidermoid cyst. True sebaceous cysts are uncommon. Epidermoid cysts are filled with keratin flakes, while true sebaceous cysts are filled with yellowish oily fluid.
A sebaceous duct cyst is in fact known as steatocystoma. Steatocystoma simplex refers to a solitary lesion predominantly seen on the face, while multiplex refers to multiple lesions. These cysts often have compressed sebaceous or oil glands in or near the cyst wall.
However, both epidermoid and sebaceous cysts can appear similar on physical examination and may require a biopsy for a definitive diagnosis.
Causes
Epidermoid cysts are often the result of:
- Blocked hair follicles.
- Skin trauma, such as an injury by a needle, or skin conditions such as acne, can implant or trap surface skin cells (epidermis) into the deeper layers of skin.
- Genetic syndromes, such as Gardner syndrome and Gorlin syndrome (basal cell nevus syndrome).
- Associated with the use of drugs like imiquimod and cyclosporine.
Epidermoid cysts due to blockage of hair follicles are considered primary, while ones due to the implantation of skin cells into deeper layers of skin due to trauma or any inflammatory process are secondary.
Epidermoid cysts are not contagious and cannot spread from one person to another.
Location and age
Epidermal inclusion cysts can occur anywhere on the body, although they are most often found on the face, scalp, neck, chest, and back.
These cysts are commonly seen in people between the ages of 20 to 40. Those associated with a genetic syndrome may appear at a younger age.
Appearance and symptoms
An epidermoid cyst typically appears as a round, dome-shaped bump that is flesh-colored, white, or slightly yellowish. It may have a small opening or punctum at the center, which often appears as if there is a blackhead embedded in the cyst.
The size can vary from a few millimeters to several centimeters. The size can stay the same or may gradually increase. Sometimes, over time they may become less noticeable, but as long as the cyst wall remains, it can recur.
These keratin cysts are usually painless but can become tender, red, and swollen if they become inflamed or infected. In some cases, they can rupture, releasing foul-smelling, cheesy contents, which are, in fact, keratinous debris.
Epidermal cysts are freely mobile under the skin unless they adhere due to surrounding inflammation or scarring.
Pictures
The pictures below show inflamed epidermoid cysts.
The image below shows the appearance of an epidermoid cyst when viewed under a microscope. The blue layer at the top represents the epidermis, and the pink layer beneath it is the dermis. Within this dermis layer, there is a cyst filled with keratin flakes.
Precautions
The appearance of a punctum on the cyst might make it seem like you can easily pop the cyst. However, you should never attempt to pop a cyst under the skin, as this can cause it to rupture.
This can lead to the release of the cyst’s contents into the deeper layers of the skin, resulting in an inflammatory reaction. It can also make the removal of the cyst wall more difficult.
Complications
Although generally harmless, epidermoid cysts can lead to the following complications.
- Infected cyst: Sometimes, a cyst may become infected and can turn painful. This may require drainage and antibiotic treatment.
- Ruptured cyst: Epidermoid cysts can rupture, causing inflammation and potential scarring.
- Cancer: It is a rare occurrence, but an epidermoid cyst can sometimes develop into skin cancer such as squamous cell carcinoma.
If your cyst suddenly grows in size, becomes red, is very painful, or has a visible discharge, it’s best to see a doctor.
Look-alikes
Several skin lesions can resemble epidermoid cysts in appearance. Distinguishing between these various types of growths is essential for appropriate diagnosis and treatment. Here are some common look-alikes:
1. Lipomas
Lipomas are benign fatty tumors that are generally soft, and round, with a rubbery consistency, and can be easily moved under the skin when touched. Unlike epidermoid cysts, lipomas don’t typically have a central punctum and are not filled with keratin. Instead, they are composed of fat cells.
Diagnosis often involves a physical examination, and if there’s any doubt, imaging studies or a skin biopsy can be performed. Treatment is usually not required unless the lipoma causes discomfort or grows large enough to be problematic, in which case surgical removal is an option.
2. Dermoid cysts
Dermoid cysts are more complex and, in addition to stratified squamous epithelium in the cyst wall, they contain other adnexal structures like hair follicles and sweat glands.
Unlike epidermoid cysts, which are commonly seen in young adults, dermoid cysts may be present at birth or become apparent during the first few years of life.
3. Pilar cysts
Pilar cysts can look very similar to epidermoid cysts but primarily occur on the scalp. They are thought to arise from the external hair root sheath and are filled with keratin. The walls of pilar cysts are thicker, making them less susceptible to rupture compared to epidermoid cysts.
Microscopically, they are characterized by the absence of a granular layer in the cyst wall and contain dense pink keratin. Treatment of these cysts is usually not necessary unless they become inflamed, infected, or problematic due to their size or location.
4. Steatocystoma
Steatocystoma, also known as a sebaceous duct cyst, can also present as skin-colored or yellowish nodules under the skin. Unlike epidermal cysts, which contain keratin, steatocystomas are filled with an oily, yellowish fluid, and often have compressed sebaceous glands within or adjacent to the cyst wall.
It usually presents as multiple bumps on the skin (steatocystoma multiplex), and less often as a single lesion which is called steatocystoma simplex.
Diagnosis
A doctor can often diagnose these cysts based on their location and a physical examination. Imaging studies such as ultrasound may help in some cases.
To confirm a diagnosis, your doctor may perform a skin biopsy and send the tissue to a pathology lab.
Do cysts go away?
Epidermoid cysts do not go away on their own. In some cases, if inflamed, they may appear bigger, and as inflammation subsides, the size may decrease, but they do not completely go away. The only way to completely get rid of them is by removal of the entire cyst wall.
Treatment
Treatment is often not necessary unless the cyst becomes problematic due to size, location, or infection.
The different treatment options include:
- Incision and drainage: The cyst contents can be drained, leaving the cyst sac in place. However, the cyst will eventually fill up with contents again. Note: Do not try to drain or burst the cyst at home as it can lead to complications such as infection.
- Steroid injection: If the cyst is inflamed, a steroid injection may reduce the inflammation.
- Antibiotics: If the cyst is infected, your doctor may prescribe antibiotics.
- Surgical excision: This involves the surgical removal of the entire cyst, including the sac. Your doctor will numb the area before excising the lesion. The area where the incision is made may leave behind a scar. Removal of the entire cyst wall will prevent the recurrence of the cyst.
Can you prevent them?
There are no definitive measures to entirely prevent epidermoid cysts. Diet and skincare ingredients usually do not have a direct impact on the prevention of these cysts.
Avoiding skin trauma and managing skin conditions may help reduce the risk of developing cysts related to these specific factors.
Key points
Epidermoid cysts are benign skin growths originating from the epidermis and are filled with keratin. They differ from true sebaceous cysts, which are filled with an oily yellowish material.
They are generally harmless but can cause complications if they become infected or rupture. Treatment is often not necessary but may include drainage or surgical removal if the cyst becomes problematic.
While epidermoid cysts are usually harmless, any new or changing skin growth should be examined by a healthcare provider for an accurate diagnosis and appropriate management.
References
- Hoang VT, Trinh CT, Nguyen CH, Chansomphou V, Chansomphou V, Tran TTT. Overview of epidermoid cyst. Eur J Radiol Open. 2019 Sep 5;6:291-301. doi: 10.1016/j.ejro.2019.08.003. PMID: 31516916; PMCID: PMC6732711.
- Kamra HT, Gadgil PA, Ovhal AG, Narkhede RR. Steatocystoma multiplex-a rare genetic disorder: a case report and review of the literature. J Clin Diagn Res. 2013 Jan;7(1):166-8. doi: 10.7860/JCDR/2012/4691.2698. Epub 2013 Jan 1. PMID: 23449619; PMCID: PMC3576779.
Disclaimer: This article is for information purposes only and does not replace medical advice.