The myth that the four common tastes of sweet, sour, salty and bitter are located at different regions of the tongue has existed for more than a century.

It arose from studies in the late 19th and early 20th century that indicated sensitivity for bitter was best at the back of the tongue.

Sweet was best tasted on the sides near the front, salty was most sensitive at the front and sour could be tasted most on the sides near the back of the tongue.

The myth began because the original data was misinterpreted.

In fact, the early studies showed each of the four tastes could be sensed at each of the regions but with modest sensitivity differences.

These differences were overlooked over time to wrongly indicate there were four distinct regions on the tongue –one for each of the tastes.

This powerful myth continues to circulate, even in a current medical textbook.

Researchers began to debunk the myth in the 1970s. Since then several studies have shown all four tastes can be sensed in all four regions, as indicated in the earlier studies.

Interestingly, despite the renewed interest there is no universal agreement about the most sensitive areas for each taste.

In the two most comprehensive studies, sensitivities for sweet and salt were slightly better at the front and side of the tongue and sour was slightly better on the side towards the back. This fits with the original research.

Resolving the argument over the taste sensitivity of different parts of the tongue is complicated by several factors.

The number of cells that serve the two main nerves in the tongue (the chorda tympani at the front and the glossopharyngeal at the back) differ from person to person.

This means the number of cells each of the nerves activates varies markedly between individuals. But how these two factors affect the sensitivity of tongue regions has not been resolved.

Age can also affect sensitivity in different regions.

Children have more taste buds in the tip of the tongue than adults and so are more sensitive to sweetness than adults on the tip.

Elderly people in their seventies exhibit little difference in sensitivity in the front, side and back regions for each taste.

The age of participants in studies is clearly important.

Another factor in measurements of taste sensitivity is the density of taste cells. This varies dramatically across the tongue, with high density correlating with high sensitivity.

Accordingly, different results have been obtained in different studies because the size of the area stimulated – and therefore the number of cells stimulated – have differed across studies.

We can only conclude that the tongue is more complicated than it appears, but there’s little doubt that the myth that special areas of the tongue sense only a particular type of taste is well and truly debunked.

Do you have a suggested topic for the Monday’s Medical Myth series? Contact the editor here.