What is lanugo?

Lanugo refers to the fine, downy hair that typically covers the bodies of fetuses during development, particularly in the third trimester of pregnancy. This soft hair serves several purposes, including providing insulation and aiding in the adhesion of the vernix caseosa, a waxy protective coating that helps to protect the skin of the fetus in the amniotic fluid. Lanugo usually disappears shortly before birth or shortly after, as it is gradually replaced by finer hairs and the skin matures.

The other choices do not accurately describe lanugo. A thick skin layer would relate more to the stratum corneum or epidermis rather than fine hair. A cheesy protective substance describes vernix caseosa rather than lanugo. Muscle tissue refers to the structural tissue that contracts to produce movement and does not relate to the characteristics of hair or skin covering the fetus.