Final answer:
The reddish purple nodules on a newborn's buttocks described during a well child visit are likely nevus simplex, a common benign condition that typically resolves without treatment. Newborn skin goes through several changes after birth, including the shedding of vernix and lanugo, and the development of softer and pinker skin as subcutaneous fat increases.
Step-by-step explanation:
The description of a new born at well child visit with 1x 0.5cm well circumscribed non-tender reddish purple nodules over the lower posterior trunk and lateral portions of the buttocks could be indicative of a common benign skin lesion in newborns known as a nevus simplex or "stork bite," which typically resolves on its own without treatment. No intervention is generally required unless the nodules persist beyond childhood or are associated with other symptoms that could suggest a more serious condition. It is important to monitor the nodules during subsequent well child visits to observe any changes in size, color, or texture.
Newborns exhibit a variety of skin conditions and characteristics post-birth, as their skin transitions from the protective environment of the womb to the external world. Right after birth, newborn skin is often coated with vernix caseosa and can show remnants of lanugo hair. The skin may appear red and wrinkled initially but gradually becomes softer and pink as the infant begins to lay down more subcutaneous fat and the skin fills out.