How does impetigo get started?

An abrasion or cut. Impetigo is a superficial skin infection. Your skin is covered with billions of bacteria all the time. It acts as a barrier to keep those bacteria out of your body. If you have an area of irritation or abrasion or cut which damages that barrier, the bacteria can cause a localized infection. If caught early, a topical antibiotic ointment may help. Otherwise oral medications may be needed.
Impetigo. Impetigo is contagious, mostly from direct contact with someone who has it but sometimes from towels, toys, clothing, or household items. After starting, impetigo often spreads to other parts of the body. This is particularly common with impetigo in children. There may be mini epidemics in day-care centers. Bacteria that cause impetigo may enter through a break in the skin.