Salicylate - An Introduction
We come into contact with salicylate in two forms:
1. Man made substances such as medicines (most notably, aspirin), solvents and perfume fixatives.
2. In its natural form in vegetables, fruit, herbs and plants.
In nature, salicylates appear to exist as a natural preservative or insecticide protecting the plant and elongating its life span. The work of Anne Swain and others in Australia in the mid 1980s demonstrated the extent to which salicylate is present in food. 
Virtually every meal we ever eat contains some salicylate and for most people this causes no problem but for an individual who is salicylate sensitive the consequences for their long term health can be disastrous. The brain is often seriously affected as an overdose of salicylate first stimulates and then depresses the central nervous system leading to emotional and behavioral problems.
A large number of symptoms and conditions have been linked with salicylate. Full details can be found in identified symptoms.
Many of the symptoms that arise as a result of salicylate intolerance mimic those of allergy but a reaction to salicylate is NOT an allergy. No current method of food intolerance or allergy testing will accurately establish salicylate sensitivity. salicylate is cumulative in the body and symptoms will only arise when the tolerance level of the individual has been exceeded (as is the case with alcohol consumption).
More information on salicylates can be found in the Salicylate Handbook.
1. Salicylates in Food. Anne R Swain et al. Journal of the American Dietetic Association Vol. 85:8 1985.