There are quite a few movies which besides being highly entertaining also touch on real science. Apart from classics such as "Hemoglobin" (aka Bleeders) with Rudger Hauer, "Antibody" starring Lance Henriksen and the all-time favored ‘Cry Onion’, the 2001 movie "Evolution" with Orlando Jones and David Duchovny stands out clearly, not least because of the appearance of an ice-cream loving geologist called Harry Block [1, 2, 3, 4]. Besides providing an adequate insight into University life for fresh(wo)men, the film also represents a fine piece of first-year chemistry and biology stretching from the depths of the Periodic Table to the secrets of evolution. Eventually, the nitrogen-based aliens are killed by a well-known peach colored anti-dandruff shampoo thanks to its content of 1% selenium sulfide.

Indeed, most of us have probably used such anti-dandruff shampoos before, yet few of us have looked at the list of active ingredients. At closer inspection, it actually turns out that nowadays selenium is notably absent in most of these preparations, which instead contain zinc-pyrithion (ZPT) as anti-dandruff agent, i.e. a zinc-complex with two bidentate sulfur/oxygen ligands [5]. According to the ‘scalp quiz’, the notorious selenium sulfide is only found in clinical strength antidandruff-defense versions [6]. In this quiz, we also find the ultimate answer to the burning question of what selenium sulfide actually is.

"What is selenium sulfide? Selenium sulfide is a powerful antidandruff active molecule which is extraordinarily effective at helping eliminate cases of severe dandruff and seborrheic dermatitis. The microfine particle has an orange color, so shampoos with selenium sulfide naturally have a peach or orange tint" [7].

From the perspective of a chemist, such an answer is, of course, likely to make you pull your hat over your shoulders. Still, as we shall see later on, the reference to microfine particles and an orange color is intriguing, as it points towards some sort of ‘mixture’ between yellow sulfur and red selenium. Indeed, the answer to the question of what selenium sulfide actually is from a chemical perspective, and thus how it, therefore, acts in a biological setting, is far from trivial. As part of this brief review, we shall try to puzzle together pieces from various scientific disciplines in an attempt to provide some answers to these questions. Since reliable biological studies involving defined species of selenium sulfide are still rare, we will necessarily focus on its chemistry first in the hope that biochemical and biological studies may follow soon.