Cleaning ourselves after an injury to keep germs at bay hampers skin's natural ability to heal itself as the bacteria living on the skin surface prevents excessive inflammation after injury.

To investigate why allergies like hay fever and eczema were less common in children from large families, who were presumably exposed to more infectious agents than others, researchers studied the nature and function of staphylococci, harmless bacteria, which lives on the skin.

It was observed that these bacteria were actually good for the human skin. Staphylococci bacterial species induced an inflammatory response when they were introduced below the skin's surface, but did not initiate inflammation when present on the epidermis (the outer layer of the skin). It was found that a staphylococcal cell wall constituent called staphylococcal lipoteichoic acid (LTA) inhibits skin inflammation. This acts on keratinocytes - the primary cells found on the outer layer of the skin.

The above findings justify why lack of early childhood exposure to infectious agents and microorganisms increase an individual's susceptibility to disease by changing how the immune system reacts to bacterial invaders.