Epidermoid cyst
An epidermoid cyst is a benign
A benign tumor is a tumor that lacks the ability to metastasize. Common examples of benign tumors include moles and uterine fibroids.The term "benign" implies a mild and nonprogressive disease. Indeed, many kinds of benign tumors are harmless to human health...

A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...

 usually found on the skin. The cyst develops out of ectoderm
The "ectoderm" is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm and endoderm , with the ectoderm as the most exterior layer...

al tissue. Histologically
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

, it is made of a thin layer of squamous epithelium
Squamous epithelium
In anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous epithelial cells...



Several synonyms exist for epidermoid cysts, including epidermal cyst, epidermal inclusion cyst, infundibular cyst and keratin cyst. "Epidermal inclusion cyst" more specifically refers to implantation of epidermal elements into the dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...

. Infundibular cyst refers to the site of origin of the cyst: the infundibular portion of the hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....

. In fact, the majority of epidermal inclusion cysts originate from the infundibular portion of the hair follicle thus explaining the interchangeable, yet technically incorrect, use of these two terms.


Epidermoid cysts commonly result from implantation of epidermis into the dermis, as in trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

 or surgery. They can also be caused by a blocked pore adjacent to a body piercing
Body piercing
Body piercing, a form of body modification, is the practice of puncturing or cutting a part of the human body, creating an opening in which jewelry may be worn. The word piercing can refer to the act or practice of body piercing, or to an opening in the body created by this act or practice...

. They are also seen in Gardner's syndrome
Gardner's syndrome
Gardner syndrome, also known as familial colorectal polyposis, is an autosomal dominant form of polyposis characterized by the presence of multiple polyps in the colon together with tumors outside the colon...

 on the head and neck. They can be infected by bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 and form a pimple
A pimple, zit or spot is a kind of acne, and one of the many results of excess oil getting trapped in the pores. Some of the varieties are pustules or papules....

-like shape.


The epidermoid cyst may be totally asymptomatic, or it may hurt when touched. It can release pus
Pus is a viscous exudate, typically whitish-yellow, yellow, or yellow-brown, formed at the site of inflammatory during infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection of pus within or beneath the epidermis is known as a pustule or...

. It is very common for women on the major or minor labia. In contrast to pilar cysts, epidermoid cysts are usually present on parts of the body with relatively little hair.

Although they are not malignant
Malignancy is the tendency of a medical condition, especially tumors, to become progressively worse and to potentially result in death. Malignancy in cancers is characterized by anaplasia, invasiveness, and metastasis...

, there are rare cases of malignant tumors arising from an epidermoid cyst.


Epidermoid cysts are usually diagnosed when a person notices a bump on their skin and seeks medical attention. The definitive diagnosis is made after excision by a pathologist based on microscopic
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

 appearance of a cystic lesion lined by cornified epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

 containing lamellated keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

 without calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...

s. They can also be seen as isointense lesions on MRI
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

 or hyperintensities on FLAIR
Flair can refer to:*Ric Flair , a professional wrestler*David Flair , his older son, also a professional wrestler*Reid Flair , his younger son, also a professional wrestler*The Flairs, an American doo-wop group in the 1950s...



Cysts can be removed by excision.

Surgical resection appears to be the mainstay of treatment; however, the extent of resection is dictated by adherence of the tumor capsule to the surrounding vital structures.
In cases where pus and blood are excreted, (particularly in those caused by body piercings,) hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 gel can be used to dry out the cyst. Patients should be aware this will slow the healing process for a new piercing.

See also

  • Sebaceous cyst
    Sebaceous cyst
    A sebaceous cyst is a term that loosely refers to either epidermoid cysts or pilar cysts . Because an epidermoid cyst originates in the epidermis and a pilar cyst originates from hair follicles, by definition, neither type of cyst is strictly a sebaceous cyst...

     (since L72.0
    ICD-10 Chapter XII: Diseases of the skin and subcutaneous tissue
    - Infections of the skin and subcutaneous tissue :* Staphylococcal scalded skin syndrome* Impetigo** Impetigo*** Bockhart's impetigo** Impetiginization of other dermatoses* Cutaneous abscess, furuncle and carbuncle* Cellulitis...

     is often mixed up with L72.1)
  • Proliferating epidermoid cyst
    Proliferating epidermoid cyst
    Proliferating epidermoid cysts are a cutaneous condition characterized by tumors that have deep invasion, and associated with anaplasia and a high mitotic rate....

  • Verrucous cyst
    Verrucous cyst
    Verrucous cysts are a cutaneous condition that resemble epidermoid cysts except that the lining demonstrates papillomatosis....

External links

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