http://www.cdc.gov/niosh/topics/body_art/more-info.html

In this article, concerns are raised about blood borne pathogens spreading in tattoo and body piercing shops. As a result of using needles that are not properly sterilized, it puts the a patron at risk of catching several viruses, one of which is the Human immunodeficiency virus (HIV).

Other viruses patrons are at risk for:
Hepatitis B virus
Hepatitis C virus
MRSA

OSHA has policies and standards put into place, as well as enforcement rules and a frequently asked questions section.