Tartrazine (otherwise known as E102 or FD&C Yellow 5) is a synthetic lemon yellow azo dye used as a food colouring. It is found in fruit squash, fruit cordial, coloured fizzy drinks, instant puddings, cake mixes, custard powder, soups, sauces, ice cream, ice lollies, sweets, chewing gum, marzipan, jam, jelly, marmalade, mustard, yogurt and many convenience foods together with glycerin, lemon and honey products. It may be found in the shells of medicinal capsules. It can also be used with E133 Brilliant Blue FCF or E142 Green S to produce various green shades (e.g. for tinned processed peas).

It appears to cause the most allergic and intolerance reactions of all the azo dyes, particularly amongst those with an aspirin intolerance and asthmatics. Reactions can include migraine, blurred vision, itching, rhinitis and purple skin patches (because of this more use is now being made of E160b, Annatto). In conjunction with E210, Benzoic acid, tartrazine appears to create an overactivity in children, and is one of the colours that the Hyperactive Children's Support Group recommends be eliminated from the diet of children.

There is an urban legend that the tartrazine in Mountain Dew causes shrinkage of testicles. Mountain Dew is a soft drink whose extreme sports advertising campaigns suggest virility in the consumer.

Tartrazine is a very commonly used colour in the United Kingdom and the United States. Use of tartrazine is banned in Norway and Austria.