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Sunscreen filters

Zinc oxide

Also listed as ZnO, mineral sunscreen, physical sunscreen, non-nano zinc oxide, nano zinc oxide

A mineral filter covering UVB and UVA, including long-wave UVA1. Photostable, rarely allergenic, and one of only three filters the FDA currently calls safe and effective.

Strong evidenceTypical strength: Up to 25% (US and EU maximum); often 10-25% as the sole filter

What it is

Zinc oxide is a white mineral powder that absorbs (and to a lesser extent scatters) ultraviolet light. Alone it covers UVB through long-wave UVA1 up to about 380 nm, which few single filters manage, and it does not break down in sunlight.

The trade-off is a white cast. Smaller ("nano" or "micronised") particles reduce the cast; coated grades keep the particles from reacting with the rest of the formula. The same ingredient is the active in many nappy-rash and skin-protectant creams.

How strong is the evidence?

Strong evidence

Zinc oxide's UV protection is measured directly in standard SPF and UVA tests, and sunscreens as a class reduce sunburn, squamous-cell skin cancer and photoageing in randomised trials. Volunteer studies show the particles stay on the surface of intact skin; a trace of dissolved zinc is absorbed, which is trivial next to dietary zinc. What is not shown: that mineral sunscreens protect better than a well-formulated chemical one at the same SPF and UVA rating.

What it's used for, checked

Broad-spectrum UVB + UVA protection

Holds up

One of the few single filters that reaches into UVA1; the SPF and 'broad spectrum' labels are what confirm the finished product works.

Suitable for sensitive or allergy-prone skin and children

Holds up

Allergy to zinc oxide is very rare, which is why dermatologists often suggest mineral filters for reactive skin and young children.

Nanoparticles get through the skin into the body

False

Repeated-application volunteer studies found particles stayed on the skin surface; only tiny amounts of dissolved zinc were absorbed.

'Reef safe'

Unproven

Some lab studies show zinc oxide particles can harm corals too; 'reef safe' is not a regulated claim.

Works well with

  • titanium-dioxide
  • bisoctrizole

Who should be careful

  • Avoid inhaling it: prefer lotions over loose powders and sprays, particularly for children. In the EU, nano zinc oxide is not allowed in products that could be inhaled.
  • Babies under 6 months: shade and clothing first; ask a clinician before routine sunscreen use.
  • A white cast can tempt people to apply less; SPF is tested at about 2 mg/cm2, and thin layers give far less protection.

The studies

Every citation is checked against its PubMed record.

  1. Support for the Safe Use of Zinc Oxide Nanoparticle Sunscreens: Lack of Skin Penetration or Cellular Toxicity after Repeated Application in Volunteers.
    Mohammed YH, Holmes A, Haridass IN, et al. · J Invest Dermatol · 2019 · Human volunteer study

    Zinc oxide nanoparticles applied repeatedly for 5 days stayed on the skin surface and in skin furrows and did not enter or harm the living epidermis; a small amount of dissolved zinc ion penetrated without local toxicity.

  2. Small amounts of zinc from zinc oxide particles in sunscreens applied outdoors are absorbed through human skin.
    Gulson B, McCall M, Korsch M, et al. · Toxicol Sci · 2010 · Human tracer study

    20 adults used isotope-labelled zinc oxide sunscreen outdoors for 5 days. The overwhelming majority of zinc was not absorbed; tracer in blood was about 1/1000 of the body's normal blood zinc. Whether it crossed as particles or dissolved zinc was not known.