zinc oxide
Meaning of zinc oxide: The white paste on a lifeguard's nose and in diaper cream, working as a physical barrier rather than as an absorbed drug.
Definition of zinc oxide
Zinc oxide is a white insoluble powder of zinc and oxygen, used on the skin as a protective barrier and as a mineral sunscreen filter. Spread as a paste, cream or ointment, it shields raw or irritated skin from moisture and friction, and it scatters and absorbs ultraviolet light. It stays on the surface rather than being taken up into the body in any quantity.
How does it protect skin?
By sitting on top of it. The particles dissolve in neither water nor skin oil, so a layer of the compound stays where it is put and keeps urine, stool, sweat and rubbing fabric off the surface underneath. That is the whole mechanism behind diaper rash pastes and the thick preparations used around wounds and stomas. Nothing is delivered into the skin, and the barrier comes off by wiping rather than by wearing off, which is why these preparations look opaque and are hard to wash away.
How does it work as a sunscreen?
The same insolubility applies. As a mineral filter it covers the full ultraviolet range, both the shorter wavelengths that burn and the longer ones tied to skin aging and to some drug reactions, which few single ingredients manage. It works from the moment it is spread rather than after a wait, and it does not break down in light, so it needs none of the stabilizers that chemical filters require. Finely milled grades look transparent instead of chalky white, a cosmetic difference rather than a chemical one.
How does it compare with other zinc preparations?
| Form | Dissolves in water | Typical use |
|---|---|---|
| Zinc oxide | No | Skin barrier and sunscreen |
| Zinc sulfate | Yes | Zinc replacement by mouth or by drip |
| Calamine | No | Soothing lotion, largely zinc oxide with iron oxide |
| Zinc pyrithione | Poorly | Antidandruff shampoo |
Only the soluble forms supply zinc the body can use, so an oxide paste spread on skin does nothing for zinc deficiency and nothing for immune function. Breathing the fume given off when zinc is heated, as in welding and foundry work, is a recognized industrial hazard that causes a short flu-like illness called metal fume fever, an entirely different matter from applying the powder to skin.
Also known as
Used in a sentence
A zinc oxide barrier paste was applied to the excoriated skin around the stoma.
Good to know
Zinc oxide does not dissolve and is not absorbed in useful amounts, so it neither corrects zinc deficiency nor supports immune function, and inhaled zinc oxide fume from hot metalwork causes a transient illness rather than any benefit.