BMJ Group Medical Reference
This is a treatment you paint on to your warts every day. You can also get plasters or pads that have salicylic acid in them. It works by slowly destroying the hard skin that makes up the wart. It also irritates your skin, and some doctors think that this may stimulate your body's immune system to fight off the wart.
There are several different medicines that contain different amounts of salicylic acid. The type you use depends on the kind of wart you need to treat.
You can buy wart treatments that contain salicylic acid from a pharmacy. Bazuka gel, Cuplex, Duofilm, Occlusal, Salactol, and Salatec form a film over the wart. Verrugon is for warts on the soles of your feet ( verrucas). It doesn't form a film over your wart, so you have to keep the treatment in place using a plaster. 
As well as using salicylic acid, you should gently rub away the surface of the wart with a file or pumice stone once a week. You may have to use this treatment for about three months.  For these reasons, some people find salicylic acid treatments difficult to use and slow to work. 
One big summary of research (a systematic review) looked at results from six studies.  Three-quarters of people who used this treatment found that at least one of their warts cleared up. People had to use the treatment for six to 12 weeks to get rid of their warts.
However, the study also showed that half of the people who used a dummy treatment (a placebo) also found that at least one of their warts cleared up.
Another study suggested that salicylic acid may not work as well as freezing for most types of warts.  However, several studies found that both treatments worked about the same for warts on the sole of the foot (verrucas).  
Salicylic acid can irritate the skin around your wart.  This isn't usually serious. Some salicylic acid gels can mark or stain, so be careful not to get them on your clothes or carpets.