Molluscum contagiosum is extremely common in children of preschool-age and elementary school-age.
The scarcity in adults, even parents with very close contact with their infected children, suggests nearly universal exposure and long-lasting immunity to the virus.
Discrete, dome-shaped, flesh-coloured to erythematous papules, frequently with a central umbilication, are characteristic. They may look like pustules on casual examination but are solid to palpation. They may be located anywhere but are common in the axillae, sides of the trunk, abdomen, face, thighs, and buttocks. They may appear like skin tags in intertriginous areas. Secondary infection or a host inflammatory response to the virus may result in large, erythematous, painful papules or pustules. Surrounding dermatitis is very common and may be difficult to treat until the lesions are gone. Lesions around the eye may cause conjunctivitis.
Clinical diagnosis is usually very easy, although finding mollusca within a sea of keratosis pilaris may be challenging. Folliculitis, skin tags, warts, and milia can usually be excluded on clinical grounds. Dermatitis may dominate the clinical picture and the individual mollusca may be hidden within the scaling erythema of atopic dermatitis. Very large mollusca may look like epidermoid cysts. A KOH smear of a molluscum examined microscopically is diagnostic but requires some experience and is seldom necessary. Biopsy is rarely needed and the pathologic diagnosis of mollusca is usually a surprise finding when some other entity was suspected.
Mollusca contagiosa are caused by a DNA poxvirus. Infection is usually spread via person-to-person contact but may spread via fomites.