I am not an expert on the topic, but I have learned about this when I was in college. My understanding is that the medical community admit they were wrong about overemphasising cleanliness decades ago and it backfired. Not exposing children to dirt at a healthy dose caused the immune system to overreact leading to allergy and other immune disorder. As someone who was sheltered growing up, that may explain my eczema. I also get hay fever as an adult even though when I wasn’t before, when I was younger.