|Systematic name||2-Hydroxy-benzoic acid|
|Molar mass||Molar mass::138.123 g/mol|
|Appearance||Fine white crystals|
|CAS number||CAS number::69-72-7|
|Density and phase||[[Density::1.44 g/cm3]], solid|
|Solubility in water||1 g/100 ml (37°C)|
|Melting point||Melting point::136°C|
|Boiling point||Boiling point::211°C|
Salicylic acid is a plant hormone now considered to be critical for many plants. It also fights off harmful pathogens that could potentially injure the plant. This acid has been found in trees such as the wintergreen, the sweet birch, the willow, and many fruits such as strawberries, cherries, apples, oranges, and others.
It is perhaps best known as the active ingredient in “Aspirin”. Salicylic acid has been used for medicinal purposes for over thousands of years. The ancient Assyrians and ancient Egyptians used it to help with headaches and other such aches and pains. Native Americans who lived in California used the bark of the willow tree in their tea to aid in the remedy of certain ailments such as fevers and swelling. Salicylic acid can be found in ointments, creams, and lotions to help in the reduction or curing of acne, psoriasis, warts, calluses etc. It is also in a popular pill form which aids in fever and swelling reduction, headaches, and the typical aches and pains.
Salicylic acid is a hormone contained within some plants that has quite a large impact on plant cell growth and development. It also aids in the processes of photosynthesis, transpiration, the uptake and transportation of certain ions, and other critical processes. Plants use salicylic acid to aid in defense against certain pathogens. The acid produces "pathogenesis-related proteins" which is the primary substance fighting the pathogens. It is involved in the systemic acquired resistance [SAR] in which a pathogenic attack on older leaves causes the development of resistance in younger leaves, though whether SA is the transmitted signal is debatable. 
Salicylic acid can be found in certain plants in the form of esters. These plants include the leaves of a wintergreen tree, the sweet birch, and others. This acid can also be found in many fresh fruits that people eat everyday. Fruits such as, raspberries (both black and red forms), strawberries, currants, apricots, plums, black cherries, peaches, grapes, crab-apples, ordinary apples, and oranges. Grapes contain about 0.32 mg of acid per kg of the fruit. Crab-apples contain about 0.24 mg of acid per kg of the fruit. Plums contain about 0.28 mg of acid per kg of the fruit. Cherries contain about 0.40 mg of acid per kg of the fruit. Currants contain about 0.57 mg of acid per kg of the fruit.  Salicylic acid can also be found in willow trees. The state of California contains a number of different species of willow trees. Species such as the Red Willow, the Mono Willow, the Arroyo Willow, and others. These plants can be found in the form of shrubs but are most often found as trees. They are commonly found in riparian environments (these are areas or environments that are close to or in the vicinity of water, such as lakes or rivers. It has been noted that even in the times of the pioneers and the Native Americans, people would search for places for water by looking for willow trees. 
Salicylic acid can be used in many skin care products. Such as creams, lotions, and other such products. It can be used to treat acne, psoriasis, calluses, warts, pilaris, corns, and many more. It causes the skin or epidermis of humans to come off more readily and easily which works accelerated new cell growth. It is also found to be a key ingredient in some shampoos that specialize in dandruff control. But, what salicylic acid is probably most well known for is the fact that it is used in many pain killers such as Aspirin. People all over the world use aspirin and other salicylic acid based pain killers for headaches, as a fever reducer, and for common everyday aches and pains. 
Salicylic acid has been used for thousands of years for its medicinal properties. Records of its use extends as far back as the times of the Assyrians and ancient Egyptians. It has continued to be a primary product in the medical fields from the civilizations of ancient Greeks through today. There are even recordings of Indians in California using the bark of the willow tree (another source where salicylic acid can be found) in their tea to treat headaches, fevers, and the everyday aches and pains.
A pharmaceutical professor at the University of Munich, by the name of Johan Andreas Buchner, in 1828, was the first person to discover that salicylic acid was the main compound of willow bark. Buchner was followed by the work of Hermann Kolbe. Kolbe was a professor of chemistry at Marburg University. In 1859 he isolated the chemical structure of salicylic acid while achieving its synthesis.
While salicylic acid had its many many benefits to people of old, it did, however, come with a couple uncomfortable side-effects for some people. The most often occurrence of these was the typical stomach irritation. However, two German scientists, by the names of Wilhelm Siebel and Felix Hoffmann, were successful in modifying salicylic acid into a form that was more tolerable to not only the stomach, but other parts of the body as well. Created between the years of 1890 and 1899, this variation was known as acetylsalicylic acid. It was late renamed to the common and contemporary title of today known as "Aspirin". Aspirin is now being used all over the word as a cure and remedy for all kinds of ailments. It is used in the treatment of headaches, an anti-inflammatory agent, fever reduction, and the relief of the general and the typical everyday aches and pains.
-  Wikipedia, Salicylic Acid
-  American Chemical Society, Journal of the American Chemical Society
-  A Survey of Medicinal Plants, Salix: History
-  A Survey of Medicinal Plants, Salix: Habitat