People often forget that one of the most crucial components of the immune system is the skin. Though it is less intricate and flashy as antibodies, complement, neutrophils, lymphocytes, and, one of my favorites, natural kill cells, the skin is an essential barrier that stymies many pathogens.
This fact is why Band-Aids are important.
Anything that causes a breach in the skin--be it a laceration, an IV, or a puncture--is the equivalent of leaving the door open to pathogens.
One ornate welcome mat recently in the news is the tattoo. Tattoos, when applied with dirty needles, have been associated with hepatitis C infections but a recent advisory was issued warning of the possibility of infection from certain bacterially-contaminated tattoo inks. In particular, non-tuberculous mycobacterial infections are the main risk. It is thought that dilution of inks with tap water introduces bacterial contamination. Mycobacterial infections are particularly hard to diagnose and often require prolonged courses of treatment.
I once heard the expression "peeing on the birthday cake" and it seems to be a particularly apt way to describe what the inconsiderate Mycobacteria are doing to people's tattoos.