FD&C Yellow #5, or tartrazine, is one of a small number of food color additives listed as certifiable by the U.S. Food and Drug Administration. It is also known as E102 in Europe.
Tartrazine, like many synthetic colorings, is an azo dye derived from coal tar. Its chemical name is 4,5-Dihydro-5-oxo-1-(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-1H-pyrazole-3-carboxylic acid.
This dye can cause allergic reactions such as hives, migraine, itching, and blurred vision. It is more likely to affect people with asthma or with aspirin intolerance. Some people claim a connection with ADD, but controlled studies haven't been able to show a connection.