There are many skin conditions that can be mistaken for each other. One of those conditions is Molluscum Contagiosum, which is a viral infection that is usually not dangerous but draws a lot of attention because of its name, and the characteristics of the lesions in the skin.

What is molluscum contagiosum?

Molluscum contagiosum, also called water warts, is an infection that gets its name from the name of the virus that causes it. There are four subtypes of molluscum contagiosum virus (MCV):¹

• MCV-1 causes most of the cases (98%), mainly in children
• MCV-2 is associated with HIV infection
• MCV-3 and MCV-4 are associated with cases in Australia and Asia

The virus can be transmitted by direct skin-to-skin contact, or by contact with things that were used by someone with lesions, such as towels, razors, toys, and others. Additionally, a person with the infection can infect themselves by touching the lesions and then touching another part of their body. Although it is present all over the world, the virus is more common in humid places. 

Children are prone to getting the infection in swimming pools, but it can be present in everybody ². In adults, it is related to sexual transmission or with a weakened immune system, such as in persons with HIV.

Clinical features

The lesions are named mollusca, they can be the same colour of the skin, pink or white. At first, the lesions are like spots, between 2 to 5 millimetres in size that appear together in the same region of the skin, they then evolve into little dome-shaped bumps (papules) with a pearly appearance and a cheesy material inside, they are usually very itchy and tender to the touch. Depending on the characteristics of the person and the cause of the lesions, they can appear in different regions of the body:^{2, 3}

• In kids, the lesions can appear on the armpits, behind the knees, or other folds of skin
• When there is a sexual transmission, the lesions are commonly in the lower abdomen, genital area and thighs
• In persons with a weakened immune system, more lesions can appear, they can be bigger, and can be spread out in different parts of the body, or appear in parts where they are unusual, for example, in the face or around the eyes

The lesions tend to disappear between 6 to 18 months and normally do not leave scars. Additionally, the virus is not commonly associated with other signs or symptoms.^3,4

Diagnosis 

The diagnosis requires questioning factors that might be associated with getting the infection, such as the recent use of swimming pools. In addition, a physical exploration of the lesions is necessary. In special cases, for example in persons with a weakened immune system, a skin biopsy is sometimes required ³ to evaluate the possibility of complications associated with the low activity of the immune system.

Skin conditions with similar presentation

A comparison between the lesions of molluscum contagiosum and lesions caused by other causes is developed below. Nevertheless, it is important to highlight that for an accurate diagnosis, a medical diagnosis by a physician is necessary.

Viral infections

• Chickenpox: Although both diseases cause spots that evolve into papules, in chickenpox, the lesions change to blisters. Additionally, in chickenpox, high temperature (fever) appears before the lesions do, these normally start in the face and torso and then spread out to the rest of the body; in molluscum contagiosum, the lesions are usually located in specific parts of the body
• Herpes Simplex Virus (HSV): These viruses cause recurrent painful blisters, which appear in the mouth, lips, or genital area after direct contact with lesions in the skin. Differently to Mollusca, the blisters tend to be unique, or bigger and are accompanied by high temperature, a general feeling of being unwell and/or a headache
• Warts: These lesions are small, skin-coloured lumps that can be present in different parts of the body. They are caused by different strains of Human Papillomavirus (HPV). When molluscum contagiosum is presented by sexual transmission it can be confused with warts because the lesions appear in the lower abdomen or genital area. However, warts have a harder consistency and Mollusca lesions are tender to palpation

Bacterial infections

• Impetigo: In this infection, the skin has red plaques covered with a yellow crust, they are referred to as golden (honey-coloured) crusted lesions. While in mollusca the colour of the lesions is like the colour of the skin, pink or white and they are individual from each other. However, it is important to highlight that impetigo can be a complication if there is a secondary bacterial infection over the lesions of molluscum contagiosum
• Folliculitis: In this condition, there is an inflammation of hair follicles, not all folliculitis is because of bacterial infection, but it is the most common cause. The skin presents bumps with pus or liquid, that are white, red or yellow. These lesions can be individual or a plaque. Unlike this condition, Mollusca can appear in places of the skin without hair follicles and the lesions tend to itch more

Other skin conditions

• Sebaceous hyperplasia: It occurs when the glands that produce sebum that is secreted through the hair follicles increase their size. They look like small bumps with the same colour of the skin, brown or yellow. Although it can happen in all parts of the body, the most common places are in the face: in the nose, forehead or cheeks. This is a big difference with molluscum contagiosum because mollusca lesions are uncommon in the face
• Acne: Although the word pimples is used to refer in general to the lesions of this condition, there are differences between them. The lesions usually appear on the face and go from open pores (blackheads), closed pores (whiteheads), and papules to pustules (papules or bumps with pus). Another difference with molluscum contagiosum is that acne lesions are not so itchy or tender
• Milia: This is the name given to a set of small lumps that appear under the surface of the skin. They are also known as cysts or milk spots. The difference with molluscum contagiosum is that milia often appear on the face, their consistency is harder, they are not itchy, and their colour is white or yellow

Treatment 

There is no specific treatment for this virus. However, depending on the location, the severity, number of the lesions, and the age of the person, there are treatments that can be offered.⁴ The most common treatment is the physical destruction of the lesions with methods such as cryotherapy or curettage. These methods are mainly used to prevent the spread of the lesions or for cosmetic reasons.

Summary 

Diagnosing skin conditions can be challenging because different causes such as viruses, bacteria or specific characteristics of the skin can produce lesions that look similar. Knowing about the different characteristics of the lesions can be helpful in recognizing what the cause for each of them is. Remember that if you have doubts about your lesions you must go to the doctor. In the case of molluscum contagiosum, mentioning, during the interrogation, about factors associated, such as the use of a swimming pool or direct contact with someone who might have the virus, is essential to help the doctor make an accurate diagnosis.