How is it that clients can share bottles of polish safely? Should I worry about cross-contamination?

You do not have to worry about cross-contamination of nail polish when it is used correctly. Scientific testing has shown that nail polish aggressively kills common pathogens that can lead to nail infections. That means when nail polish is applied to healthy nails with no visible signs of infection, it would be extremely unlikely for cross-contamination to occur. Even so, nail polish should never be applied to an infected or unhealthy looking nail plate unless a doctor has previously determined there is no risk of transmitting an infection.  If nail polish is accidentally applied to any nail plate that shows visible signs of infection, proper salon sanitation protocol dictates that the bottle should immediately be properly disposed of and not used on any other client. -- Doug Schoon is chief scientific advisor for CND