Zinc Oxide in Sunscreen Formulation
ZnO is the only single ingredient that delivers broad-spectrum UV protection (UVA + UVB, 290–400 nm) with full photostability. It scatters and absorbs UV photons through both physical and electronic mechanisms — unlike organic filters, ZnO does not degrade under prolonged sun exposure. Used in mineral sunscreens, daily-wear cosmetics, and baby/sensitive-skin formulations.
Why Zinc Oxide for This Application
Function-by-function breakdown of how ZnO contributes to the final formulation.
- Broad-Spectrum UV Coverage — ZnO uniquely covers the entire UVA (320–400 nm) and UVB (290–320 nm) range with a single ingredient — most organic filters require combinations to achieve the same span.
- Photostability — ZnO does not degrade under sunlight, unlike avobenzone and many other organic UV-A filters which require photostabilizers like octocrylene to remain effective.
- Hypoallergenic / Reef-Safe — Not absorbed transdermally at meaningful levels; not implicated in coral bleaching like oxybenzone/octinoxate. Approved as a sunscreen active under US OTC, EU Cosmetic Regulation, and CFDA.
- Antimicrobial Bonus — Mild surface antimicrobial activity contributes to natural preservation, allowing some sunscreen formulations to reduce parabens or other synthetic preservatives.
Recommended Grade & Dosage
Pair the right purity tier and surface treatment with the production process.
Pharmaceutical Grade Zinc Oxide
USP/EP/JP-compliant ZnO with low heavy metals (Pb ≤50 ppm USP, ≤10 ppm in-house tighter) and microbial limit testing (TAMC ≤10² CFU/g). Pharma grade is the regulatory baseline for any sunscreen filed as an OTC drug.
| Parameter | Value |
|---|---|
| Mineral Sunscreen | 10 – 25 wt% (SPF 30–50+) |
| Daily Wear / BB Cream | 2 – 5 wt% (modest SPF 15–25 contribution) |
| Lip Balm SPF | 5 – 10 wt% |
| Particle Size Choice | Micronized (D50 1–3 μm) for visible coverage / Nano (<100 nm) for transparency |
Formulation & Process Notes
Working parameters and process control points from production experience.
| Parameter | Value |
|---|---|
| Pre-Dispersion Required | ZnO must be pre-dispersed in oil phase with a wetting agent (caprylic/capric triglyceride + dispersant) before emulsion formation |
| Shear Equipment | High-shear homogenizer or bead mill to reach D50 <3 μm in product (Hegman 7+) |
pH Stability
ZnO is amphoteric — stable pH 6 – 8. Acidic formulas (<5.5) may slowly dissolve ZnO
| Parameter | Value |
|---|---|
| Emulsion Type | Water-in-oil (W/O) preferred for high-load mineral SPF; oil-in-water (O/W) works at <15 wt% |
| Coating Options | Silica, dimethicone, or amino acid surface treatment for improved dispersion and reduced photocatalytic activity |
Frequently Asked Questions
+Micronized vs nano ZnO — which to specify?
Micronized (D50 1–3 μm) gives full opacity (visible white cast) and is the safest choice for B2B baby/sensitive skin filings. Nano (D50 <100 nm) is transparent on skin and required for modern aesthetic formulas, but requires separate cosmetic-grade certification and may be banned in spray-on products in EU due to inhalation concerns. Specify upfront.
+What SPF can a 20% ZnO formulation deliver?
Depends heavily on particle size and dispersion quality, but typical 20% mineral SPF delivers SPF 30–50 PA+++ when properly milled to Hegman 7+. Poor dispersion can drop labeled SPF by 30–50%. ISO 24444 in-vivo testing is the regulatory standard.
+Does ZnO photocatalyze and degrade other formula ingredients?
Uncoated ZnO has mild photocatalytic activity under UVA — can degrade sensitive ingredients (vitamins, certain emollients). Surface-coated grades (silica, dimethicone, or stearic acid coating) suppress this and are strongly recommended for daily-wear cosmetics with vitamins or actives.
+Is ZnO compatible with chemical UV filters?
Yes — modern combination sunscreens use ZnO + organic filters (avobenzone, ethylhexyl methoxycinnamate, or newer Tinosorb actives) to achieve high SPF at lower total active load. Compatibility is generally good, but check pH stability and consider coated ZnO to prevent photocatalysis of avobenzone.