Baby acne, also known as acne neonatorum, is a conition that affects roughly 20% of newborn babies. Lesions appear at around 2 weeks postpartum and commonly disappear after 3 months. Lesions include small, red, papules, which mainly affect the cheeks, as well as the nasal bridge of infants. Infants usually develop neonatal acne because of stimulation of the baby's sebaceous glands by lingering maternal hormones after delivery. These hormones cross the placenta into the baby and after delivery they cause the oil glands on the skin to form bumps that look like pimples. Baby acne usually clears up within a few weeks, but it can linger for months.