Molluscum contagiosum (MC), sometimes called water warts, is a viral infection of the skin and occasionally of the mucous membranes. MC can affect any area of the skin, but is most common on the trunk of the body, arms, groin, and legs. It is caused by a DNA poxvirus called the molluscum contagiosum virus (MCV). MCV has no non-human reservoir (infecting primarily humans, though equids can rarely be infected). The virus that causes molluscum contagiosum is spread from person to person by touching the affected skin. The virus may also be spread by touching a surface with the virus on it, such as a towel, clothing, or toys. Risk factors include being sexually active, and those who are immunodeficient. Four types of MCV are known, MCV-1 to -4; MCV-1 is the most common and MCV-2 is seen usually in adults. Approximately 122 million people were affected worldwide by molluscum contagiosum as of 2010 (1.8% of the population). It is more common in children. Molluscum contagiosum is most common in children aged one to 11 years old. Some evidence indicates molluscum infections have been on the rise globally since 1966, but these infections are not routinely monitored because they are seldom serious and routinely disappear without treatment. Molluscum contagiosum is contagious until the bumps are gone. Some growths may remain for up to 4 years if not treated.