Hotel rooms aren’t yucky – you colonize them with your own personal bacteria within hours - The Washington Post

Researchers have found that not only does your body's biome (bacterial ecosystem) thoroughly mark a room to make it your territory within hours, its signature of bacteria types can be used to identify you and where you've been better than fingerprints.  They also recommend having a family dog to help establish a child's biome by passing bacteria from family members and friends.  The richer the bacteria population, the stronger a person's immune system becomes, and the fewer the allergies.