Why chemical sunscreen is a category that describes nothing

There is no polite way to put this and no need for an impolite one. Chemical sunscreen is not a chemical category. It is a marketing category that borrowed a scientific word and inverted its meaning, and the borrowing has cost the natural sun care category more credibility than any single overstated claim.

The obvious point, stated once

Zinc oxide is a chemical compound with the formula ZnO. Titanium dioxide is a chemical compound with the formula TiO2. Water is a chemical compound. Shea butter is a mixture of chemical compounds, principally triglycerides of stearic and oleic acids, plus a fraction of unsaponifiables. Every ingredient in a cosmetic product has a chemical identity, a Chemical Abstracts Service registry number, a specification and a place in a safety assessment. There is no ingredient anywhere in the category that is not a chemical, and there is no manufacturing route that is not chemistry.

This is not pedantry about words. It matters because the chemical and non chemical framing invites a reader to sort ingredients by feeling rather than by property, and once that habit is established it is very difficult to have a useful conversation about anything, including the questions where the natural category has a real case to make.

Where the usage came from

It came from a shorthand that was originally reasonable. Dermatology texts and older product literature distinguished physical sunscreens, meaning the metal oxides thought to work by physical scattering, from chemical sunscreens, meaning molecules thought to work by chemical absorption. The distinction was mechanistic, not moral, and it reflected the understanding of the time.

Two things then happened. First, the mechanistic premise turned out to be wrong: the metal oxides attenuate ultraviolet mainly by absorption too, which is set out in absorb against reflect. Second, the word chemical drifted in general usage until it meant roughly artificial and probably harmful. The shorthand survived the collapse of both its justification and its neutrality, and it is now used as a warning label.

What people are usually trying to say

Underneath the word there are normally two or three real preferences, and every one of them can be stated precisely.

• I want an inorganic filter. Precise, true, and easy to check on an ingredient list. Say inorganic or metal oxide.
• I do not want a filter that is absorbed through skin. Precise and legitimate as a preference. Worth knowing that dermal absorption differs enormously between organic filters, that the large modern ones are poorly absorbed because of their molecular size, and that detection in blood is not the same as harm.
• I want fewer ingredients. Precise. Also worth knowing that metal oxide formulas often need more supporting ingredients, not fewer, because dispersions are difficult to stabilise.
• I want to avoid a specific substance. The most precise of all. Name it. Ingredient lists are standardised and searchable, and an INCI name is unambiguous in a way that a category name never is.

Every one of those is a better sentence than chemical free, and every one of them is checkable.

What the word costs the people who use it

A category that describes its competitors as chemical cannot then object when its own claims are read loosely. If words are being used for their emotional charge rather than their content, all words in the conversation lose value, including the accurate ones. When a natural brand says its formulation is gentler, a reader who has already been told that competing products are chemicals has no way to distinguish that claim from the last one.

It also concedes the argument that the category most needs to win. The strongest case for a mineral formulation is a formulation case: particular skins tolerate a particular film better, some people want a product with a shorter and more legible ingredient list, some parents prefer a filter that has been in wide use for a very long time. Those are arguments about substances and their properties. They are chemistry arguments. Framing the choice as chemistry against nature throws them away.

Dose, and the point that is usually skipped

Toxicology assesses substances at exposures. A substance is not safe or unsafe in the abstract; it has a dose response relationship, a route of exposure, and an assessed margin of safety in a defined use. A cosmetic safety assessment estimates how much of a product is applied, how often, over what area, how much of an ingredient could reach systemic circulation, and compares that with the level at which no adverse effect was observed in study. That is what the numbers on a permitted list represent.

None of this is available to a reader who has decided that substances are either chemicals or not. It is available to a reader willing to look up a filter by name. The Scientific Committee on Consumer Safety publishes its opinions in full, including the parts where the committee says the data are insufficient. Those documents are more useful, and considerably more sceptical, than most of what is written about them.

The other half of the pair

Chemical only works as a category because it is set against natural, and natural in cosmetics is not a defined term either. There is no legal definition of a natural cosmetic product in Great Britain, no threshold that a product must meet, and no regulator that adjudicates the word. Private standards exist and set their own criteria, and those criteria are frequently generous about chemical modification of plant derived material. A substance can be counted as being of natural origin after several synthetic steps, provided the carbon skeleton started in a plant.

This is not a scandal. It is a reasonable engineering compromise, because unmodified plant material rarely behaves in a formulation. It does mean that natural, on a pack, tells you which standard the maker chose to follow rather than what is in the tube. That is examined at length in what natural means in cosmetics.

The pairing therefore sets an undefined word against a word that means everything. It is difficult to construct a less informative axis, and the fact that it dominates how sunscreen is discussed is a genuine loss, because there are real differences between products that a shopper could act on and none of them are visible from where this axis puts them.

What to do instead

Use inorganic and organic, which are the actual chemical classes. Use metal oxide when you mean zinc oxide or titanium dioxide. Use particulate and dissolved when the physical state is the point. If you object to a specific substance, name the substance. And when a product tells you what it is free from, treat that as information about the marketing rather than about the formula, because free from claims are constrained by the advertising codes precisely because they are so often used to imply a hazard that has not been established.

This publication uses inorganic and organic throughout, and treats mineral as a category name in commerce rather than a term in chemistry. Where the word chemical appears here, it means what it means in chemistry.