The Elements You Touch Every Day

Between waking up and leaving the house you will make skin contact with something like twenty elements, most of them without noticing and several of them in forms chosen specifically because of a chemical property. This is not a survey of what is in your possessions. It is narrower and more literal: the elements your hands and mouth actually touch on an ordinary morning, and why each one is the element that ended up there.

Fluorine and tin, before you are properly awake

Toothpaste is a surprisingly dense piece of applied chemistry. The active ingredient is a fluoride salt — usually sodium fluoride, sometimes stannous fluoride, which is a tin compound. Fluorine is there because the fluoride ion substitutes into the hydroxyapatite of tooth enamel to form fluorapatite, which dissolves less readily in acid. It is the smallest and most electronegative of the halogens, and the substitution works because the fluoride ion is almost exactly the right size to sit where a hydroxide ion was.

Stannous fluoride does the same job and additionally interferes with bacterial metabolism, which is why it appears in pastes sold for gum health. Its drawback for decades was that it stained teeth, and reformulating around that took a long time.

The white colour is titanium dioxide, and the gritty part is silica — silicon dioxide, the same compound as sand and glass, milled to a particle size that abrades plaque without abrading enamel.

Chlorine, calcium and a public health argument in your tap

The water is disinfected with chlorine, or with chloramine, and the reason that specific element won out over every alternative is residual action: chlorine keeps working all the way through the distribution network rather than only at the treatment plant. Ozone is a better disinfectant and does not survive the journey.

Whether the water leaves limescale in the kettle depends on how much calcium and magnesium it picked up passing through limestone or chalk. Hard water is not a contaminant; it is a geological signature of the aquifer underneath you.

The metals you grip

Most of the metal surfaces in a house are one of four things.

• Stainless steel — iron with at least around 11 per cent chromium, and usually some nickel. The chromium is the whole point: it reacts with air to form a chromium oxide film a few atoms thick that seals the surface and re-forms instantly if scratched. Ordinary steel rusts because iron oxide flakes off and exposes fresh metal underneath.
• Brass — copper and zinc, on door handles, keys, taps and locks, chosen originally because it machines beautifully and does not corrode.
• Galvanised steel — a zinc coating on iron, on everything from bins to nails. Zinc protects the steel even where the coating is broken, because it corrodes preferentially. The whole structure is a battery with the zinc deliberately sacrificing itself.
• Aluminum — foil, window frames, cookware, drink cans. What your fingers rest on in every one of those cases is not the metal but its own oxide, a film far too thin to see; aluminum covers how something that high on the reactivity series gets away with being wrapped around a sandwich.

Nickel belongs on this list for the opposite reason to everything else on it: it is the one element here that a sizeable minority of people cannot touch without consequences. Nickel carries the prevalence figures and the regulation that followed them. The part that matters for a morning is where the exposure actually comes from, which is almost never an object anyone thinks of as nickel — it is the stainless fork, the plated key, the coin and the watch case, none of which announce their alloy.

Sodium, iodine and the most successful additive in history

Table salt is sodium chloride, which is unremarkable until you look at what was added to it. Most salt on most shelves carries a trace of potassium iodide or iodate, and has done since the 1920s, because inland soils are stripped of the element and a thyroid cannot work without it. Iodine sets out the deficiency figures and the country-by-country history of the programme.

What earns it a place in a list of things you touch is the delivery mechanism, which is the genuinely clever part. Nobody had to change a habit, take a supplement, remember a dose or buy a new product. The additive rode into every kitchen on a commodity that was already sitting there, at a per-person cost too small to be worth working out. Almost nothing else on this page was engineered into a household by stealth, and nothing else on it was engineered into a household at all.

What is in your pocket

Modern coinage is mostly not made of what its name suggests. Since 1982 a United States cent has been 97.5 per cent zinc by mass, wearing only a copper skin, and the coin called a nickel is three-quarters copper. Euro coins use several distinct alloys of copper, aluminum, zinc, tin and nickel, partly so that vending machines can tell them apart electromagnetically.

Copper's presence in coinage predates any of that reasoning by three millennia, but it has been retrospectively justified: copper surfaces are genuinely antimicrobial, and the mechanism — copper ions disrupting bacterial membranes — is well characterised.

The pen in the same pocket almost certainly has a ball of tungsten carbide in its tip, roughly a millimetre across, because it needs to be harder than paper and wear-resistant over kilometres of rolling contact.

The element that makes everything white

If you touched anything white today, you probably touched titanium dioxide. It is the most-produced white pigment on Earth, and it is in paint, paper, plastics, sunscreen, toothpaste, tablets and food colouring. Its virtue is an exceptionally high refractive index, which makes it scatter visible light so efficiently that a thin layer becomes opaque.

Its predecessor was lead white, and the changeover is why a white surface is now a safe thing to put a hand on; titanium and lead between them set out what that swap cost and what it saved. What is worth noticing from inside a single morning is the sheer breadth of it. Paint, paper, plastic, sunscreen, toothpaste and the coating on a tablet are the same compound, so the odds are good that you made contact with it four or five separate times before you reached the front door, in materials with nothing else whatsoever in common.

Phosphorus, and a match that killed the people who made it

The striker strip on a matchbox contains red phosphorus, mixed with powdered glass. Red phosphorus is one of the element's allotropes: a polymeric form, stable in air, quite different in behaviour from white phosphorus, which is the same element with the atoms arranged as discrete P₄ molecules.

White phosphorus was what early matches used, and it caused phosphorus necrosis of the jaw among match factory workers — "phossy jaw", a disfiguring and often fatal occupational disease that became one of the defining industrial scandals of the Victorian era. The 1888 London matchgirls' strike was fought partly over it. White phosphorus in matches was prohibited by the Berne Convention of 1906, which the United Kingdom enacted in 1908. It is one of the earliest examples of an international treaty banning a specific chemical from a specific product.

You are also made of them

Six elements account for about 99 per cent of your body by mass: oxygen at roughly 65 per cent, carbon at 18, hydrogen at 10, nitrogen at 3, calcium at around 1.5 and phosphorus at about 1. Calcium and phosphorus are there almost entirely as the mineral phase of bone, which is a good reminder that the distinction between chemistry and biology is bookkeeping rather than physics.

Every one of them was chosen for a property

The elements in daily contact were not chosen at random or for cheapness alone. Fluorine is in toothpaste because the fluoride ion is the right size to replace hydroxide in enamel. Chromium is in cutlery because its oxide heals itself. Zinc coats steel because it corrodes first. Titanium dioxide is in white things because it scatters light better than the alternative that used to poison people. Iodine is in salt because salt is the one thing everybody buys.

Every one of those is a specific property of a specific element, and in most cases nothing else in the table would do the job.