Post puberty humans begin to secrete a substance called Sebum which changes the neutral PH of our skin from ~7 to 4.5-5.5. This has that advantage of serving as a protective line against pathogens and discourages larger organism like lice. My question is given these benefits, why are children not born with these advantages?

  • $\begingroup$ Kids don't have many dermal infections, mostly flu, respiratory and digestive infections. the acid mantle didn't prevent the black death fleas and the flu epidemics. $\endgroup$ Commented Mar 26, 2019 at 1:51
  • $\begingroup$ This question is wrong. Sebum isn't a "protective line", in fact excess sebum production (an exceedingly common problem) invites pathogenic bacteria to feed, causing acne and pimples. I don't see any evidence of sebum protecting against lice. See my question at medicalsciences.stackexchange.com/questions/13862/… for an explanation of how damaging puberty is for skin. $\endgroup$ Commented Mar 31, 2019 at 3:21
  • $\begingroup$ @user1258361 The Acid Mantle is a very well accepted phenomenon subject to a great deal of peer-reviewed research (see here: ncbi.nlm.nih.gov/pubmed/30125885). The prominence of Lice on children is acceptably attributed to the lack of the acid layer, but if you have a source that suggests otherwise, please provide. And your linked question is somewhat irrelevant, excess of anything is negative, that doesn't negate the positive effects that proper distribution has. $\endgroup$ Commented Mar 31, 2019 at 4:36
  • $\begingroup$ You -do- realize that secretion of cetylpyridinium chloride would be a far superior barrier against pathogens, right? $\endgroup$ Commented Apr 1, 2019 at 17:07
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    $\begingroup$ I'm fairly certain that constant contact with cetylpyridinium chloride would result in quite a few negative side-effects, and I'm certain that the human body doesn't have the mechanism needed to synthesize cetylpyridinium chloride. $\endgroup$ Commented Apr 2, 2019 at 3:43


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