Zinc oxide

Zinc oxide is the thick white paste on a lifeguard’s nose, the ingredient in most nappy rash creams, the mineral in a mineral sunscreen and a white pigment besides. It is one substance doing several jobs, and the job it is doing changes what the label must tell you.

Why the percentage is printed

This is the most useful thing on the page, and it generalises well beyond zinc.

Most personal care products are cosmetics, and a cosmetic ingredient list gives order without amount. But a product that claims to protect skin or to filter UV is making a claim about affecting the body, which in US law makes it an over-the-counter drug.

Drugs carry a Drug Facts panel, and the labelling rule requires topical products to state the proportion of each active ingredient.

So the regulations set the range and the panel prints the number:

As a sunscreen, zinc oxide is permitted up to 25 percent, alongside Titanium dioxide at the same ceiling.

As a skin protectant, it is permitted at 1 to 25 percent.

A nappy cream that says 40 percent zinc oxide has told you something no ordinary cosmetic label ever does. That contrast is the whole subject of the cosmetics label guide, and zinc is the cleanest example of it.

What it does not raise

No animal origin question. It is a mineral, and one of the small set of ingredients on this site that closes rather than opens, like Calcium carbonate.

No fragrance question in itself. What reacts on skin in a zinc-based cream is very often something else in the formulation rather than the zinc, which is the argument for reading the whole list rather than stopping at the active.

Non-nano, which is a marketing phrase

Products advertise non-nano zinc oxide, and it is worth being precise about what that is and is not.

It describes particle size, which affects how white the product looks on skin and is the subject of an active research literature on absorption. It is not a term defined in the US sunscreen or skin protectant regulations, which set concentration limits and say nothing about particle size.

So a non-nano claim is a manufacturer’s description rather than a regulated category. That does not make it meaningless, and it does not make it a standard. Telling those two apart is the habit the guide to unregulated label words is built around.

What makes it a drug, exactly

The regulation defines a skin protectant drug product as one that “temporarily protects injured or exposed skin or mucous membrane surfaces from harmful or annoying stimuli”.

That is a definition built entirely on what the product claims to do. The same white mineral in a foundation, doing nothing but making it opaque, is a cosmetic ingredient with no percentage anywhere on the pack.

So the printed number is not a property of zinc oxide. It is a consequence of the claim on the front of the box, and that is a genuinely useful thing to know when two products list the same ingredient and only one of them tells you how much.

Calamine, incidentally, is listed as its own separate active in the same regulation at 1 to 25 percent, so a calamine lotion carries a percentage for the same reason.