The phrase "unwanted invaders" refers to people or things that come into a place without permission or welcome. They may disrupt or cause harm in that place. Full definition
Silver is your body's natural secret weapon against unwanted invaders. (activationproducts.com)
For example, gut microflora serves as a significant barrier to infection from outside pathogens, preventing unwanted invaders such as food toxins, toxic chemicals, bad bacteria and fungi from entering our systems. (thebark.com)
The best defense against fleas - and other unwanted invaders like heartworms - is good, overall health. (pesthacks.com)