Molluscum contagiosum (mo-LUS-kum kun-tay-jee-OH-sum) is a fairly common skin infection caused by a virus. It causes round, firm, painless bumps ranging in size from a pinhead to a pencil eraser. If the bumps are scratched or injured, the infection can spread to nearby skin. Molluscum contagiosum also spreads through person-to-person contact and contact with infected objects