Petrolatum

Petrolatum does one thing extremely well: it sits on skin and stops water leaving. Nothing formulated since has beaten it at that, which is why it is still in nappy creams, lip balms, wound dressings and the hands of every dermatologist recommending an ointment over a lotion.

It also has an origin that makes people uneasy, and a second name in the regulation that is worth understanding.

Two entries, one substance

The US skin protectant regulation lists petrolatum at 30 to 100 percent, and then lists white petrolatum separately, at the same range, as its own active.

Two entries for what is essentially the same material at different degrees of refining. White petrolatum is the more purified grade, which is where the word white comes from and why it appears on the products meant for broken skin and for infants.

Mineral oil is listed in the same regulation too, at 50 to 100 percent. It is the liquid fraction of the same refining, which is why the two behave alike and why a cosmetic list often carries both.

Since a protection claim makes a product an over-the-counter drug, the percentage is printed in the Drug Facts panel. In an ordinary moisturiser making no such claim, petrolatum sits in the ingredient list with no number at all, which is the split covered on Zinc oxide.

The petroleum question

Petrolatum is derived from crude oil, and that is the whole basis of the unease.

Two things are true about it and both should be said.

It is not the crude. Cosmetic and pharmaceutical grades are refined to remove the aromatic compounds that carry the concern, and the pharmacopoeial grades exist precisely to specify that. The concerns that circulate attach to unrefined or poorly refined material.

Nothing on a label proves the grade. The INCI name is Petrolatum whether or not it meets a pharmacopoeial standard, so a reader wanting the purified grade is relying on the manufacturer and the market rather than on the ingredient list. A product listing white petrolatum, or naming a pharmacopoeial standard, has told you more than one listing petrolatum alone.

That is an honest limit rather than a reassurance, and it is the same shape as most of what the cosmetics label guide deals with.

What it does not raise

No animal origin. It is mineral, so it is vegan by composition, which is unusual company for something this widely distrusted.

No fragrance or preservative question in itself. Pure petrolatum contains no water, so it needs no preservative at all. That is the practical reason it turns up on lists of things to try when a reaction has no obvious cause: it is one of the shortest ingredient lists available. The page for skin that reacts to everything explains why that matters when you are eliminating candidates.

For nappy rash

Petrolatum and Zinc oxide are the two workhorses here, and the regulation permits them in combination.

The difference is mechanism rather than strength. Petrolatum seals; zinc oxide sits on the surface and is mildly astringent. Products use one, the other, or both, and the panel tells you which and how much.

Where the answer is not on the label is whether a particular rash needs something else entirely, and that is a health visitor, pharmacist or doctor rather than a scan. The page for parents is deliberately narrow about that.