Here's one little gem from Dr Susan Prescott's 'The Allergy Epidemic,' which I'd recommend to anybody who has even a passing interest in allergies and their recent increase. It surprised me by its readability, which perhaps the following quote (from the middle of one of the more technical chapters) doesn't demonstrate very well. But bear with me.
... exposure to allergens through the oral route (the gut) is more likely to induce immune tolerance... there is some evidence that immune cells in the gut are more likely to suppress allergic responses, compared with the same kinds of cells in the skin or the respiratory tract. (pg 49)
Did you catch that? I'll paraphrase:
The immune cells in our guts are better at telling the difference between things they need to react to and things they don't, than the cells in our skin or lungs are.
Which means that the best and safest way to teach our immune systems to operate properly is to get lots of different particles in our mouths.
So what do babies do? Put everything in their mouths. Yes, it's how they learn about objects, but now we find out it's teaching their immune systems too.
God really has designed human beings very, very well.