This study is designed to compare the skin lipid and protein composition between term and premature infants and determine how the skin composition changes over the first four weeks of life. The investigators hope to elucidate the unique characteristics of premature skin by measuring the lipid and protein content in skin, how it changes during the first month of life, and how it varies with formula feeding versus breast feeding. Additionally, the investigators will study the relationships among diet, skin composition and plasma lipids in premature infants over the first four weeks of life.

Infants in the UCDMC Neonatal Intensive Care Unit with no congenital or acquired diseases of the skin or cardiovascular system will be enrolled after informed consent has been obtained from their parents. This is an observational study with no intervention. Procedures: At enrollment, 2 weeks and 4 weeks of age, skin lipids will be collected using three methods. First two small pieces of blotting paper (2 cm x 2 cm) will be placed on the infant's skin, one on the left side of the abdomen just above the umbilicus and one on the left inner thigh. The blotting paper will be left in place for 15 seconds and then removed. Second, two adhesive discs will be placed on the skin, one just below the umbilicus and one on the right inner thigh. The discs will be left in place for 30 seconds and then removed. Third, two areas of skin, one on the right side of the abdomen just above the umbilicus and the other on the inner right thigh, will be gently swabbed with sterile cotton swabs (one for each location). The intent is to remove a thin layer of oil/lipid from the skin upon removal of the paper or the adhesive disc or with swabbing without disrupting the skin surface (similar to taking a fingerprint). Blood specimens will be obtained three times, each time 1 ml : once at enrollment, at 2 weeks and the last one at 4 weeks of age, to generate a plasma lipoprotein profile and size distribution (HDL, LDL, VLDL, total cholesterol). For infants that are fed expressed human milk, we will also obtain a sample of mother's milk for analysis of lipid profile (about 2 ml).

Inclusion Criteria:

• infants who are likely to be inpatients in the NICU for at least 4 weeks

Exclusion Criteria:

• congenital or acquired skin disease,
• cyanotic congenital heart disease,
• neonates that are not viable and
• those with lethal anomalies such as anencephaly, trisomy 13, trisomy 18, renal agenesis

Newborn infants in the NICU at UCDMC. 20 neonates will be enrolled, 5 in each of the following gestational age categories: 23-27 weeks, 28-32 weeks, 33-36 weeks, >36 weeks. Infants will be involved in the study from enrollment until 4 weeks of age or until discharge, whichever comes first.