A common mistranslation: half-life

Yes, Half-Life is a video game! And a very good one! As is its derivation Counter-Strike. But unfortunately for our geek readers, this is not what we are going to talk about... We will explain where the scientific concept of half-life comes from in order to understand why it is so commonly mistranslated.

Where does the concept of half-life come from?

In the pharmaceutical industry, and especially in pharmacokinetics, half-life is an extremely common concept as it measures a basic characteristic of drugs: the speed at which they are eliminated from the body. The shorter the half-life, the faster the drug is cleared from the body. This term originates from the nuclear industry where it describes how long it takes for radioactive atoms to decrease by a half. For instance, if there are 10 bn radioactive atoms in a sample and sample half-life equals 10 years, then there will be 5 bn radioactive atoms left after 10 years, 2.5 bn after 20 years and so on.

Figure 1: Half-life in the nuclear industry

The use of this concept is necessary when you cant tell when an exponential decay process is going to end. For instance, you cannot tell when a drug substance completely disappears from your body! You can only tell when you stop detecting it... From the moment the drug substance reaches maximum blood level, it is assumed to follow an exponential decay in the same way that radioactive atoms do. The concept of elimination half-life has therefore been introduced to measure how quickly the substance leaves the body.


Lets assume maximum blood concentration of a drug substance (for injection) is 1,500 ng/mL and its half-life is 3 hours. As soon as the substance is injected, blood concentration increases and reaches a maximum after a while. Then 3 hours after that, the blood level of the drug substance will be 750 ng/mL. And 3 hours later, it will be 325 ng/mL, and so on.

Figure 2: Half-life in pharmacokinetics

How is half-life translated, or mistranslated into other languages?

It is now clear to everyone that half-life means how long it takes for something to decrease by a half. Therefore, any attempt to translate it should maintain the original meaning of half. In Spanish, a mistranslation has expanded and is now commonly used in the pharmaceutical industry, especially in Latin America. It is now very common to read vida media, which literally means average life, in cases where the concept at hand is clearly half-life... In Spanish, medio(a) means half only when it comes before the noun (e.g.: medio kilo de patatas = half a kilogram of potatoes). But in vida media, media undeniably means average. Too bad!

Here is how vida media de eliminacin is defined on Cubas official pharmaceutical glossary: Parmetro farmacocintico que representa el tiempo que tarda la concentracin de un frmaco en disminuir a la mitad de su valor inicial. Well, they are actually talking about half-life... This is just an example, but there are many more...

Where does the Spanish mistranslation come from?

This error is believed to originate from a translators mathematical confusion between half and average. A translator with an even basic scientific background would not have gotten mixed up between these two fairly basic concepts. Fortunately, the most mathematically accurate translation for this term, that is semivida, is also still the most common one!

But Wordreference is not helping at all by putting this mistranslation in first position. Come on, guys! People believe in you... Sadly, Wordreference has become the main reason why translators mistranslate half-life...

Figure 3: Is Wordreference always a reference?

Does this mistranslation exist in other languages?

Since France is a country where the nuclear industry has always played an important role, it has always been adequately translated by demi-vie. In Portuguese, half-life has also been adequately translated by meia-vida or semi-vida. In Italian too, with emivita, the prefix -emi being equivalent to -hemi in English, as in hemisphere, meaning half-sphere. German translation Halbwertszeit literaly means the time (Zeit) it takes for a value (Wert) to decrease by a half (Halb), which is just perfect!

Should Spanish translators keep translating half-life by vida media?

Spanish translators still using vida media should wonder why they are alone in deciding to translate half-life by the Spanish equivalent for average life. They will argue that vida media and semivida are too different concepts. Well, maybe they are, but in pharmacokinetics, the second one is the only relevant one! They may also use the excuse that translators love so much: there is not only one translation for a term. As honest and truthful as it sounds, it is most of the time just a sloppy excuse. Yes, in translation, right and wrong may exist sometimes... By the way, what do you do everytime you have to translate mean half-life? Vida media media, right? Or Vida media promedio maybe? Hardly better...