Causes of Warts
All warts are caused by strands of the Human Papilloma Virus (HPV). The virus strands that cause warts are transmitted via skin-to-skin contact. These strands generally live on everyone's skin, and warts appear based on a person's immunity to the virus. Thus, if you touch someone's wart, you will not get warts yourself unless you lack the immunity to the virus in that area of your skin.
Goal of Wart Treatments
The only thing that can truly kill warts is your body's own immunity. When you have a virus or bacterial infection inside of your body, your immune system kicks in right away to combat it, so you aren't sick for endless periods of time. However, according to the Mayo Clinic, the immune system in the skin functions mainly in the dermis, which is below the epidermis, where warts grow. This makes it harder for your body to detect them. While there are many treatments out there, including cryosurgery, salicylic acid compounds, and even the DIY method of "suffocating" the warts with nail polish or duct tape, these measures really only help to get the body's own immunity to recognize the virus.
Benefits of Salicyclic Acid
When you treat a wart topically, you are instigating an immune response, as is evidenced from the blistering that usually forms around the area, regardless of the method you choose. Essentially, the goal of any wart treatment is to get the body to realize that there is a viral infection on the skin surface, which needs attention. Salicylic acid is used for many skin conditions and is safe to use on warts in relatively high concentrations. This makes it a good option for wart treatment because it is an aggressive over-the-counter treatment. Moreover it is a good treatment to try first because it is not as harsh on the surrounding skin as cryosurgery and has a better success rate than other methods. It is also inexpensive, non-invasive, and with it you can treat yourself in the privacy of your own home.
Salicylic acid is a weak beta hydroxy acid. It is used in concentrations of about 17 percent to treat warts, because the outside of a wart is often very rough. Salicylic acid's exfoliating properties slough away the outer layers of the wart and act to try and kill accessible parts of the wart. Often when you use salicylic acid, you will notice redness at the site of your wart, and it may be tender to touch. This is actually the response you want because it means that the immune system recognizes that there is something going on at the site of the wart.