A baby's skin rash is diagnosed by noting the symptoms and then comparing those to the signs of known conditions, according to WebMD. Dry patches, pimples, spots of various colors, yellowish skin and greasy crusts are all signs of baby rashes that typically heal on their own.
Salmon patches and pink pimples on a baby's skin are caused by maternal hormones in the womb, and they may last weeks or even months, notes WebMD. Small, white bumps on the face are signs of blocked oil glands that fade away once the infant's glands enlarge. Yellow colored skin is a symptom of jaundice that sometimes requires further attention. Red, itchy patches of skin are caused by eczema that is treated with skin conditioners, gentle soaps and sometimes a steroid cream like hydrocortisone. An intense red rash with small bumps around the edges that appears on skin under a diaper may be a sign of a fungal infection.
An infant's skin is prone to many common rashes that are harmless, but some require immediate attention, says WebMD. Blisters filled with yellowish, opaque fluid may indicate a serious bacterial infection or herpes. Red or purple dots spread across a baby's body may be caused by a bacterial or viral infection. Any rash on a newborn baby's skin that is associated with cough, fever, lack of appetite or lethargy should be evaluated by a doctor.