Wednesday, September 17, 2008

Apple #341: Lanugo Hair

A friend of mine had a baby recently, and we were talking about the baby's hair. What color had it been when she was born two months ago, what color it is now, what color it might come to be over the next year. Then my friend told me that babies typically have hair when they're in the uterus, except that hair covers the fetus' entire body. She said it goes away before the baby is born.

I said, "Where does it go?"

She looked at me, her eyes widening and said, "I don't know."

Then we launched into all kinds of speculation about what might have happened to that hair, but it was less than palatable, so I won't go into it. But this conversation definitely roused my curiosity.

  • Around the fifth month of pregnancy, a fetus will grow hair all over its body. But this isn't the kind of hair we born-people have. It has no pigmentation and it's ultra-fine and soft.
  • It's so soft that it feels downy. In fact the word "lanugo" is Latin for "down," like a baby duck's downy feathers.

This is a fetus at 30 weeks. You can just barely make out the lanugo on the fetus' head. Some vernix (see below) is caught in the fetus' eyebrows.
(Photo from Calgary Youth For Life
-- lots of pictures here of fetal development)

  • Nobody is completely certain of the purpose of lanugo, but there are two theories:
  1. Helps to maintain the fetus' body temperature in the womb
  2. Helps to keep the vernix in place. The vernix is a white gooey, some say cheesy fluid, which is made up of oil secreted by the fetus' oil glands (we have lots of those on our faces) and the fetus' dead skin cells. The purpose of the vernix is to help protect the fetus' skin from the amniotic fluid (think about being in a bath for 9 months and what that would do to your skin!). In fact, the word vernix comes from a Latin word which means "fragrant varnish." When the baby is born, along with the amniotic fluid and some blood and stuff, this is some of the goo that the doctor wipes off. As far as the lanugo goes, some people think that the fine hair helps to keep the vernix close to the skin. But the fact that the lanugo falls out before the baby is born seems to contradict this theory, because the baby is still going to need that vernix for another month or two.

Newborn, with goo
(Photo from Solar Navigator)

  • Around the 7th or 8th month, the lanugo hair falls out. Babies that are born prematurely may still have their lanugo. About 33% of babies that are born full-term still have it. But in almost all cases it will fall out after the first month or so.

Baby born with the lanugo hair still present.
(Photo from Hub Pages)

  • Just as nobody knows for sure the purpose of lanugo, nobody is 100% certain what happens to it after it is shed because they haven't actually seen where it goes. But scientists think that the baby ingests it -- the hair would be floating around in that amniotic fluid, after all -- because after the baby is born, that hair is part of the baby's first bowel movement.
  • That first bowel movement has a fancy name: meconium. It's made up of all the stuff that the fetus has ingested in the womb but doesn't need: skin cells, mucus, amniotic fluid, bile, water, and the lanugo hair. It has a fancy name because it's unlike any other bowel movement a human being will have in the rest of his or her life because never will we ingest such a cocktail of substances again. It's really gooey and tarry, but it also contains no bacteria so it has no odor.
  • (The origins of the word "meconium" are misleading. Aristotle thought that the first bowel movement helped keep the fetus asleep, so he named it "meconium," which means "poppy juice," which was a way of saying he thought it was an opiate. Which it is not. Aristotle did make a few mistakes.)

Hub Pages, What is Lanugo?
Babies Online, Baby, Pregnancy, and Parenting Information, Lanugo
Pregnancy, How Will My Newborn Look?, Hair Follicle Embryogenesis
Indiana University, A Moment of Science (AMOS), Lanugo Hairs, Pregnancy & Parenting, Lanugo and Vernix
NationMaster Encyclopedia, Meconium
OneLook dictionary search, lanugo, vernix, meconium


  1. This blog entry creeps me out in a way I haven't experienced since watching the movie "Freaks" for the first time.

  2. Well, apparently we're all a little freaky from before the time we're born.

  3. D: as if babies didn't freak me out enough...


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