The widespread belief is that one should not scratch an itch as this may lead to infection. Seems pretty obvious and I'm sure there's plenty of evidence of the truthfulness of this idea. But if that's so, then why has evolutionary selection pressure resulted in the experience of the itch sensation and the behavior (desire) to scratch it? Certainly, if such behavior was in the main more dangerous from an infection and disease standpoint, it should have been swiftly deleted from the gene pool of our species (and all the other species that also display this innate behavior, such as most other primates, as best as I can tell).
When I scratch an itch, I note that secretions appear on the skin's surface, sealing it and I hypothesize initiating an immune response. Does this better train the immune system over the course of an organism's lifetime, and improve its odds for reproduction? Is there some other key survival benefit for which the itch response is a necessary tag-along, getting a free ride over the course of natural selection? I think there is some unrecognized value to the instinct of scratching one's itches.
We have learned in recent years that children raised in a protected sterile setting often develop asthma or other improper immune responses, and that those raised on farms do better--subjected to many immune system challenges. I wonder if scratching one's itches falls into the same category and has a value the medical profession is ignoring.
