The primary reason to swab the skin with alcohol is to clean the injection site, and provide some antiseptic mechanism. The 30 second dry time is to allow the evaporation of the alcohol to kill as many bacteria on the skin as possible.
I've noticed comments about not swabbing, and it makes zero sense to not swab. I've seen comments about swabbing or not swabbing for lab work or an IV. Again, foolish.
Even with swabbing, there is a very small risk of getting an abscess with a sub-Q or shallow IM injection, but there is no valid reason to not swab with alcohol or chlorhexadine prior to lab work or initiating intravenous access of any kind. This is a direct pathway into the bloodstream, bypassing the defenses we have in our layers of skin.
As a medical professional of 17+ years, both Critical Care and ER, I question the professional veracity of anyone who claims to be a medical clinician and states it's fine to not swab for lab work or similar venous access.
Evidence? Blood cultures drawn on what seem to be properly prepped skin, e.g. cleansed with chlorhexadine or povidine/iodine, sometimes come back "contaminated" with skin flora, which is why when blood cultures are drawn, 2 sets are taken, as it is highly unlikely that both sets of cultures would be contaminated with skin flora. If that bacteria can travel into the culture bottle, it can also be introduced into the blood stream.
