This Reddit post answers the question 'Why can't the immune system fight off the bacteria that causes acne?'. So instead, I ask a more general one as entitled above.

I am conjecturing that the body has methods to detect the excess of Propionibacterium acnes bacteria. If correct, then e.g., why cannot the body open skin pores to unclog oil?
Surely the body can do something better than forming pimples and pus?

1 Answer 1


This is the anatomy of a hair follicle

enter image description here

You can see that there is no muscle to control the size of the pore where the hair exits the skin, so there is no way that the body can control normally the size.

The primary problem is not with the Propionibacterium acnes but with excessive oil production which then causes a blockage in conjunction with dead skin creating a fertile environment for the bacteria to proliferate.

Commensal bacteria on the skin are not controlled by the immune system ( white cells, antibodies, complement etc can't migrate through intact skin to reach the bacteria ) but by competition with other bacteria, moisture etc.

Oil or sebum production is driven by sex hormones testosterone, 5-testosterone (DHT) and 5-androstene-317diol, and unless there's some evolutionary advantage to do so, there won't be any selection for those individuals who less likely to produce excessive oil. Since male hormones are important, then evolution may be selecting more for those with high male hormone levels which produces more of an advantage then the temporary disadvantages of acne.

  • Thanks. But your penultimate paragraph raises an immediate question: Why does not the body then reduce oil production?
    – user14
    Commented Apr 25, 2016 at 3:39
  • Would you please respond in your answer, which is easier to read than comments?
    – user14
    Commented Apr 25, 2016 at 3:39
  • 2
    @LePressentiment I think he already answered your question: The reproductive advantage of male hormones outweighs the disadvantage of acne. Therefore, there is no selective pressure for the body to reduce oil production.
    – Carey Gregory
    Commented Apr 26, 2016 at 4:13
  • 1
    @LePressentiment The simple answer: because it doesn't know it should. These types of responses are trained through evolution. A similar example would be that many venoms are lethal if and only if they spread throughout the bloodstream. A number of chemicals produced by the body, known as vasoconstrictors, are used in certain cases (like when the body is at risk of hypothermia) to restrict blood flow in certain areas. Why, then, doesn't the body naturally restrict blood flow after snake bites in the bitten areas? Because there was never enough evolutionary pressure to develop this reaction. Commented Apr 26, 2016 at 4:48

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