Salicylic acid is a natural phenolic compound known as the active principle of aspirin.
March 1 2016

Source of salicylic acid
This phenolic compound is found in fruits and vegetable. A high intake of produce can increase blood levels of salicylic acid. 

Benefit of salicylic acid
It is possible that the beneficial effects of regular fruit and vegetable consumption could be due to low chronic salicylic acid exposure.

Front Plant Sci. January 2014. Regulation of water, salinity, and cold stress responses by salicylic acid. Salicylic acid (SA) is a naturally occurring phenolic compound. SA plays an important role in the regulation of plant growth, development, ripening, and defense responses. The role of SA in the plant-pathogen relationship has been extensively investigated. In addition to defense responses, SA plays an important role in the response to abiotic stresses, including drought, low temperature, and salinity stresses. It has been suggested that SA has great agronomic potential to improve the stress tolerance of agriculturally important crops. However, the utility of SA is dependent on the concentration of the applied SA, the mode of application, and the state of the plants (e.g., developmental stage and acclimation). Generally, low concentrations of applied SA alleviate the sensitivity to abiotic stresses, and high concentrations of applied induce high levels of oxidative stress, leading to a decreased tolerance to abiotic stresses. In this article, the effects of SA on the water stress responses and regulation of stomatal closure are reviewed.

Topical salicylic acid is often used in dermatologic conditions because of its keratolytic, bacteriostatic, fungicidal, and photoprotective properties. The bioavailability of salicylic acid differs depending on the vehicle used and pH of transcellular fluids. Although rare, salicylic acid toxicity (salicylism) can occur from topical application.

Toxicity
J Am Acad Dermatol. 2014. A review of toxicity from topical salicylic acid preparations. Topical salicylic acid is often used in dermatologic conditions because of its keratolytic, bacteriostatic, fungicidal, and photoprotective properties. The bioavailability of salicylic acid differs depending on the vehicle used and pH of transcellular fluids. Although rare, salicylic acid toxicity (salicylism) can occur from topical application. Physicians should be mindful of the potential for salicylism or even death from topically applied salicylic acid.