The exact cause of baby acne is unknown. Acne is usually the result of clogged pores. When your pores clog, a pimple can develop. Providers suspect that baby acne is the result of hormonal changes that affect your newborn during birth or the first few weeks of their life. Hormones in the placenta can affect how your baby’s skin produces sebum. Sebum is an oily substance that the sebaceous glands in your baby’s skin make to protect their skin and hair. Too much sebum can clog pores and lead to acne. In addition, babies have sensitive skin when they’re born. Their skin may react negatively to anything that’s left on it for too long, especially if they have food, vomit or drool residue on their skin.