What is molluscum contagiosum?
Molluscum contagiosum is a common viral skin infection of childhood that causes localised clusters of umbilicated epidermal papules.
Who gets molluscum contagiosum?
Molluscum contagiosum mainly affects infants and young children under the age of 10 years. It is more prevalent in warm climates than cool ones, and in overcrowded environments. Adolescents and adults are less often infected.
Molluscum contagiosum tends to be more numerous and last longer in children who also have atopic dermatitis, due to deficiencies in the skin barrier. It can be very extensive and troublesome in patients with human immunodeficiency virus (HIV) infection or that have other reasons for poor immune function.
What causes molluscum contagiosum?
Molluscum contagiosum is caused by a poxvirus, the molluscum contagiosum virus. There are at least 4 viral subtypes.
There are several ways the virus can spread:
- Direct skin-to-skin contact
- Indirect contact via shared towels or other items
- Auto-inoculation into another site by scratching or shaving
- Sexual transmission in adults.
Transmission of molluscum contagiosum appears to be more likely in wet conditions, such as when children bathe or swim together. The incubation period is usually about 2 weeks but can be as long as 6 months.
What are the clinical features of molluscum contagiosum?
Molluscum contagiosum presents as clusters of small round papules. The papules range in size from 1 to 6 mm and may be white, pink or brown. They often have a waxy, shiny look with a small central pit (this appearance is sometimes described as umbilicated). Each papule contains white cheesy material.
There may be few or hundreds of papules on one individual. They mostly arise in warm moist places, such as the armpit, behind the knees, groin or genital areas. They can arise on the lips or rarely inside the mouth. They do not occur on palms or soles.
When molluscum contagiosum is autoinoculated by scratching, the papules often form a row.
Molluscum contagiosum frequently induces dermatitis around them and affected skin becomes pink, dry and itchy. As the papules resolve, they may become inflamed, crusted, or scabby for a week or two.
Complications of molluscum contagiosum
- Secondary bacterial infection from scratching (impetigo)
- Conjunctivitis when the eyelid is infected
- Disseminated secondary eczema; this represents an immunological reaction or 'id' to the virus
- Numerous and widespread molluscum contagiosum that are larger than usual may occur in immune-deficient patients (such as uncontrolled HIV infection or in patients on immune suppressing drugs), and often affect the face
- Spontaneous, pitted scarring
- Scarring may be spontaneous or due to surgical treatment
Spontaneous scarring due to molluscum contagiosum
How is molluscum contagiosum diagnosed?
Molluscum contagiosum is usually recognised by its characteristic clinical appearance or on dermatoscopy. White molluscum bodies can often be expressed from the centre of the papules.
Dermoscopy of molluscum contagiosum
What is the treatment for molluscum contagiosum?
There is no single perfect treatment of molluscum contagiosum since we are currently unable to kill the virus. In many cases no specific treatment is necessary.
- Picking out the soft white core (note, this could lead to autoinoculation)
- Cryotherapy (can leave white marks)
- Gentle curettage or electrodessication (can scar)
- Laser ablation (can scar).
- Antiseptics such as hydrogen peroxide cream or povidone iodine solution
- Podophyllotoxin cream
- Wart paints containing salicylic acid
- Cantharidine solution
- Under review: berdazimer gel is under FDA review with anticipated approval in early 2024.
Secondary dermatitis may be treated symptomatically with a mild topical topical corticosteroid such as hydrocortisone cream. Dermatitis is unlikely to fully resolve until the molluscum infection has cleared up.
Prevention of molluscum contagiosum infection
Molluscum contagiosum is infectious while active. However, affected children and adults should continue to attend daycare, school, and work.
To reduce spread:
- Keep hands clean
- Avoid scratching or shaving
- Cover all visible lesions with clothing or watertight bandages
- Dispose of used bandages
- Do not share towels, clothing, or other personal effects
- Adults should practice safe sex or abstinence.
What is the outlook for molluscum contagiosum?
In immune competent hosts, molluscum contagiosum is a relatively harmless. The papules may persist for up to 2 years or longer. In children, about half of cases have cleared by 12 months, and two-thirds by 18 months, with or without treatment. Contact with another infected individual later on can lead to a new crop.
Infection can be very persistent in the presence of significant immune deficiency.