Zinc oxide: sunscreen filter and diaper-rash protector

Zinc oxide might be the most versatile ingredient in your bathroom. It’s the white paste in a tube of diaper cream, and it’s also the active ingredient in many mineral sunscreens. Same powder, two very different jobs. Here’s what it does in each, what Health Canada allows, and what to make of the worries about nano particles.

What zinc oxide is

Zinc oxide is a white mineral powder made of zinc and oxygen. It doesn’t dissolve in water, it’s very stable, and it’s been used on skin for a long time. A 2014 review of zinc in dermatology describes topical zinc oxide as a long-standing soothing and sun-protecting ingredient, used in everything from diaper pastes to ulcer dressings.

Two properties explain almost everything it does:

• It sits on top of the skin. Mixed into a thick ointment, it forms a layer between your skin and whatever is irritating it.
• It blocks ultraviolet light. That’s why it’s one of the few filters allowed in both “natural” and conventional sunscreens.

Job one: protecting skin from diaper rash

Diaper rash is mostly irritation. Skin that’s wet for long stretches gets softer and weaker, and urine and stool then irritate it further. (Our guide to diaper rash explains the causes in more detail.)

A zinc oxide cream or ointment acts as a barrier. It keeps moisture, urine and stool off the skin so it can recover. The Canadian Paediatric Society recommends an unscented barrier ointment, such as petroleum jelly or a cream with zinc oxide, to protect and lubricate the area. Its practical tips:

• After a dirty diaper, clean the area, then apply the barrier ointment generously.
• After a wet diaper, reapply only if needed.
• You don’t need to scrub off every trace of cream at each change.

How strong is the evidence? The 2014 zinc review notes that zinc oxide paste has long been used for diaper dermatitis and describes it as a useful soothing, anti-itch agent, but says it’s less effective as a treatment than options such as topical corticosteroids (anti-inflammatory creams, usually prescribed or recommended by a pharmacist). In other words, zinc oxide is excellent at prevention and at protecting mildly irritated skin. It isn’t a cure for every rash.

What Health Canada allows in diaper creams

In Canada, diaper rash creams that make treatment claims are natural health products, with an NPN on the label. Health Canada’s Diaper Rash Products Monograph, updated in 2024, allows:

• zinc oxide from 1 to 25 percent in creams and other products;
• 25 to 40 percent in a zinc oxide ointment;
• use from birth onward.

Permitted claims include that the product temporarily protects and helps relieve minor skin irritation from diaper rash, and helps treat and heal it. The monograph’s directions are to apply liberally to a clean, dry diaper area as needed, and labels must tell you to stop and see a health care provider if symptoms get worse, last more than 7 days, or come back within a few days.

The Canadian Paediatric Society also advises seeing a doctor if the rash is severe, keeps getting worse despite treatment, has blisters, boils, pus or discharge, or comes with a fever. The society notes that a yeast (Candida) rash usually sits in the deepest parts of the skin folds, such as the groin; that kind of rash needs a different treatment.

Job two: filtering the sun

In sunscreen, zinc oxide is a mineral UV filter. The zinc review describes it as a broad-spectrum sunscreen ingredient, with better protection against long-wave UVA (the rays linked to skin aging) than titanium dioxide, the other mineral filter. Health Canada’s Primary Sunscreen Monograph makes the same distinction: it lists zinc oxide as protecting against both UVA and UVB, and notes that titanium dioxide alone is less effective at blocking long-wave UVA.

The monograph, updated in February 2026, allows up to 25 percent zinc oxide in a sunscreen, counting any nano form in that total. It covers babies from 6 months of age and up. For younger babies, ask your doctor or pharmacist and rely on shade and clothing.

Is nano zinc oxide safe?

To make mineral sunscreen less chalky, manufacturers use very small particles, some in the nanometre range. That raised a fair question: can particles that small get through the skin?

The evidence so far is reassuring for creams and lotions:

• The European Commission’s Scientific Committee on Consumer Safety concluded in 2012 that sunscreens with up to 25 percent zinc oxide nanoparticles are safe to use on the skin. It found the particles themselves don’t appear to penetrate, though a small amount of dissolved zinc may be absorbed.
• A 2020 review of a decade of imaging studies in volunteers, using a type of microscopy that can see into living skin, found nano zinc oxide stays on the surface and in skin folds, unlikely to get past the outermost layer, including after flexing, massage and on damaged skin. The researchers did find some zinc ions, the dissolved form, reaching living skin, and saw no signs of harm to skin cells.

The one clear exception is sprays. The European committee noted that inhaled zinc oxide nanoparticles can cause inflammation in the lungs, so it didn’t consider spray products safe. With children especially, a cream or lotion is the better choice.

Why some zinc sunscreens look white

Zinc oxide is a white powder, so larger particles show on the skin as a chalky film. The 2020 review explains that this white cast is what made zinc sunscreens unpopular, and that smaller particles made them look transparent. That’s the trade-off: bigger particles are more visible, smaller ones blend in. Both protect.

If the white cast bothers you, especially on deeper skin tones, look for a formula that goes on clear, which usually means finer particles. Whatever you choose, use enough and reapply. A sunscreen you’re happy to wear every day beats a “perfect” one you avoid.

Zinc oxide is also generally gentle, which is why it’s popular for sensitive skin. Like any product, though, the full formula matters: fragrance or other ingredients can still irritate. If a zinc cream or sunscreen causes redness or itching, stop and check with a pharmacist.

You can browse the panel’s reviewed balms and ointments or baby care products.

Zinc oxide earns its double life: a thick zinc cream protects irritated diaper skin, and a zinc sunscreen filters both UVA and UVB. Health Canada sets clear limits for each, nano forms appear safe in creams, and sprays are best avoided. If a diaper rash lasts more than a week or looks infected, see your doctor.