I've read the gist of this article in my local news org feed. What it basically comes down to is that Finnish scientists noticed that Russian children who grew up in rural areas usually had way less asthma cases than Finnish city children, and thus began to research why this was the case. They hypothesized that early (first 10000 days) exposure to micro-organisms might play a key role in training the immune system not to over-react to (harmless) micro-organisms later on in life, and thus "train" the immune system better. Their hypothesis now seems to have been validated.
Basically this comes down to the hunch I had for quite a long time: Isolating children into an almost clinical environment is not a great way to boost the immune system. This might explain why there are so many people with allergies. People living too cleanly and not getting exposed to (benevolent) micro-organisms so that their immune system prepares them when exposed to later in life. I think that's one of the reasons that kids that are around pets early in life usually have lower risk of developing allergies later on.
The reasoning went like this: We've spent most of our evolution in caves digging in dirt, and now (relatively) recently we have been transported into an environment where we can pretty much have the cleanest settings. What do you think this will do to our immune system?