If your baby's impetigo isn't treated, he may be contagious for several weeks. Once he begins antibiotic treatment and the rash starts to clear (usually after 24 hours), he's no longer contagious. In the meantime, keep your baby out of daycare and other close-contact situations.
Be vigilant about hygiene: Wash your baby's clothes, sheets, and towels every day and prevent friends and family members from sharing soap, towels, hairbrushes, or other personal items with your baby. Wear gloves when you apply his ointment, and wash your hands well afterward.
Make sure all the members of your household wash their hands regularly with soap and water. You may want to use paper towels for drying until the impetigo clears up.