Why do sweets change the colour of your tongue?

A blue lolly, a green gobstopper or a handful of red sweets can leave your tongue a very different colour. It looks alarming, but it is only a stain from the food colouring, and it soon fades.

Why the colour sticks

Sweets are coloured with concentrated colours, and when a sweet sits on your tongue for a while, some of that colour settles on the surface. Your tongue is not smooth. Its upper surface is covered in small structures called papillae, which give it its rough texture. The most numerous are the filiform papillae, fine, thread like cone shaped bumps with a tough outer layer, which cover most of the front two thirds of the tongue.

A medical case report from 2019 shows the pattern well. A dermatologist in San Diego described a man who had eaten a blue coloured gelato containing the dye brilliant blue FCF. The whole upper surface of his tongue turned blue, while the tip and the sides kept their normal colour, and there was a faint blue tinge to his upper lip.

Blue dyes

The classic synthetic blue is brilliant blue FCF, E133, a dye used in candy floss, ice cream, icings, ice lollies and sweets. In the United States it is the more common of the two approved blue food dyes. In Britain, Nestlé switched blue Smarties to spirulina, a natural blue from a blue green alga, in February 2008, and removed artificial colours from its UK sweets by 2012: see what is spirulina doing in my sweets?

Is it harmful?

The stain itself is harmless and temporary. In the 2019 case, the blue caused no symptoms and faded by itself within six hours.

There has been debate about blue dyes themselves, though. In 2013 researchers at the Slovak University of Technology tested the blue dyes brilliant blue and patent blue on pig tongue tissue exposed to human saliva containing the dyes for 20 minutes. They reported that some of the dye could pass through the upper surface of the tongue and, in their view, go straight into the bloodstream without being broken down in the gut. They tested the dyes at the maximum levels allowed, and their work was a laboratory study, not a study of children. Brilliant blue remains an approved colour, and it is generally considered safe to eat. For the wider row over artificial colours, see why do some sweets have a warning about children?

Getting it off

There is nothing you need to do. A coloured tongue fades on its own; in the 2019 case, it took less than six hours.

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