**1. Introduction**

One hundred years ago, the 29-years old scientist Albert von Szent-Györgyi was conducting observations on the biological oxidation of the adrenal cortex. After exploring different plant and animal systems, he found in turnip extracts a putative carbohydrate that inhibited the peroxidase reaction and named it hexuronic acid [1]. At the time, he would have been probably surprised to know that the identification of hexuronic acid as the anti-scurvy factor vitamin C [2] would have earned him the Nobel prize in Physiology or Medicine in 1937. Ever since those pioneer years, hexuronic acid, soon renamed ascorbic acid (AsA) to make clear also in the name its essence as the anti-scurvy factor, has been receiving much attention from researchers worldwide, and tens of thousands of studies have been published, reporting on many different aspects of this interesting molecule. In parallel with the scientific literature, vitamin C encountered unprecedented popularity: today a simple google search of "vitamin C" returns over 210 million hits. Finding one's way in this ocean of information, sometimes contradicting, is not easy. It is perhaps necessary to recapitulate the main steps of this long story and tell facts from opinions, if possible. Already in its early years, AsA showed some kind of a "dual nature", acting both as a reducing agent (antioxidant) and a protectant from the dreadful disease known as scurvy [3–5]. The aim of this contribution is to present evidence in support of the hypothesis that the two "faces" of AsA coexist and are both parts of an efficient signal transduction mechanism allowing living organisms to sense their environment and successfully adapt to variable conditions.
