What is a cyst?
A cyst is an abnormal growth–usually benign (noncancerous)–that contains a liquid or semi-liquid material enclosed in a membrane.
Skin cysts appear as dome-shaped lumps few millimeters to several centimeters in size. They may be firm or fluctuant and movable.
Non-inflamed cysts are painless and covered by a normal, white or yellow skin. Some cysts may ooze a white or yellow greasy material.
Inflamed cysts can be covered by red skin and can be tender or painful. They may ooze pus and they may burst.
A cyst can slowly grow or heal on its own.
Skin cysts are more common in adults than in children . Rarely, they can be present from birth; in most cases they develop after puberty.
How do skin cysts form?
The exact cause of a skin cyst is often not known. Common causes and risk factors include:
- An injury
- A surgery
- High testosterone levels
- Use of androgenic anabolic steroids
- A genetic predisposition
A cyst in the skin develops when certain cells of the skin or the skin glands excrete the material, which from some reason cannot be cleared. An example is a small injury that blocks the opening of the sebaceous gland.
Types of Skin Cysts
Picture 1. Multiple chalazions in both eyelids (source: University of Iowa, Health Care, CC licence)
2. Dermoid Cyst
Dermoid cysts are developmental abnormalities that appear mainly in small children as soft lumps around the eyes, on the neck or scalp . They can contain skin cells, hair follicles and sweat glands .
Picture 2. A. A dermoid cyst near the right eye B. Surgical removal of the cyst (source: Plastic and Aesthetic Research, CC licence)
Picture 3. An epidermoid cyst (source: Samuel Freire da Silva, MD, Atlasdermatologico.com.br)
4. Eruptive Vellus Hair Cyst
Eruptive vellus hair cysts arise from the blocked hair follicles . They appear as small (2-3 mm) red or brown papules, mainly in the middle of the chest. They develop in children or teenagers and can spontaneously disappear.
Picture 4. An eruptive vellus hair cyst (source: DermNetNZ, CC licence)
Picture 5. Two pilar cysts on the scalp (source: DermNetNZ, CC licence )
6. Pilonidal Cyst
Pilonidal cysts usually develop in the skin in the tailbone area due to repeated irritation, for example, in drivers.
Picture 6. A pilonidal cyst over the tailbone (source: Samuel Freire da Silva, MD, Atlasdermatologico.com.br)
Picture 7. A large sebaceous cyst on the back of the hand (source: ResearchGate, CC licence)
Steatocystoma simplex (one cyst) or multiplex (multiple cysts) is a hereditary disorder in which, at puberty, some hair follicles and sebaceous glands develop into soft semi-translucent bumps, 2 mm – 2 cm in size, mainly on the chest, but also on the abdomen, upper arms, armpits or face .
Picture 8. Multiple steatocystomas on the upper arm (source: DermNetNZ, CC licence)
A doctor (dermatologist) can usually recognize a cyst by an inspection. After a cyst removal, a pathologist usually checks the removed tissue and tells, what exact type of cyst it is and is it cancerous.
Examples of bumps and lumps that can look similar to skin cysts :
- Boil or furuncle (see bumps at the back of the neck)
- Branchial cleft cyst (on the side of the neck)
- Digital mucous cyst (on the fingers)
- Ganglion cyst (near the wrist or other joints)
- Ingrown hair
- Lipoma (a benign tumor at the shoulder girdle level)
- Perianal abscess (between the buttocks; in Crohn’s disease)
- Parotid gland tumor (below the ear)
- Rheumatoid nodules (on the hands in rheumatoid arthritis)
- Skin cancer (a flat red bump with an ulcer)
- Swollen lymph node (in the neck, armpits or groin)
- Syringomas (small benign sweat gland tumors, in adolescent Asians, around the eyes, belly button or in the armpits) 
- Thyroglossal duct cyst (in front of the neck)
- Xanthoma (accumulation of fat near the elbows, knees, heels or buttocks)
What is a pseudocyst?
A pseudocyst, unlike a true cyst, does not contain epithelial cells in the membrane but just the fibrous tissue.
An example of a skin pseudocyst is nodulocystic acne, which can develop as a complication of acne vulgaris.
A doctor can remove a cyst by a small surgical procedure, which includes local anesthesia, a cut in the skin and removal of the cyst’s content and membrane.
- Oakley A, Cutaneous cysts and pseudocysts DermNetNZ
- Turnbull N, Eruptive vellus hair cysts DermNetNZ
- Ngan V, Dermoid cysts DermNetNZ
- Sabhalok SS et al, 2016, Epidermoid and dermoid cysts of the head and neck region Plastic and Aesthetic Research
- Oakley A, Nodulocystic acne DermNetNZ
- Oakley A, Steatocystoma multiplex DermNetNZ
- Oakley A, Syringoma DermNetNZ