Why is it so important to not scratch eczema patches on the skin?

Eczema is inflamed skin, and inflamed skin itches. The problem is that the skin is already an inflamed, compromised skin barrier due to things like pathogens, viruses and fungus. If you start scratching and mechanically disrupt the surface of the skin, you've now added a second insult to an already inflamed or open skin barrier. The result is denuded, scratched, excoriated skin that is open to a whole host of pathogens in the environment.