What is the absorption rate of zinc oxide?

Zinc Oxide Absorption Rate

Zinc oxide has minimal systemic absorption when applied topically, with absorption rates estimated to be less than 0.03% of the applied dose. 1, 2

Absorption Characteristics of Zinc Oxide

Topical Application (Sunscreens and Dermal Products)

• Zinc oxide nanoparticles (ZnO-NPs) accumulate primarily on the skin surface and within skin furrows without penetrating into viable epidermis 2
• Studies using traceable forms of zinc (68Zn) have shown that while trace amounts may be detected in internal organs after topical application, this does not significantly alter total zinc concentration in major organs 3
• The skin penetration of zinc oxide is extremely limited, with most particles remaining on the skin surface 2, 4
• Even with repeated application of ZnO-NPs over 5 days, no evidence of penetration into viable epidermis or local toxicity was observed in human volunteers 2

Factors Affecting Absorption

• Particle size affects absorption properties:
  • Nanoparticles (typically 50-150 nm) are used in sunscreens for consumer preference due to transparency 1
  • Despite smaller size, nanoparticles still show minimal skin penetration 2
• Formulation characteristics:
  • ZnO is increasingly incorporated into formulations as powders dispersed within polymeric or emollient dispersions 1
  • These formulations promote adequate spreadability while deterring aggregation and agglomeration 1

Safety Profile of Topical Zinc Oxide

• Risk assessment studies indicate that zinc oxide is safe for use in cosmetic products within regulatory limits (up to 25% concentration) 5
• Even with repeated dermal application at high doses (up to 1,000 mg/kg body weight), no significant adverse effects were observed in animal studies 4
• The margin of safety (MOS) for zinc oxide in sunscreens has been estimated at 448.2, well above the threshold for safety concerns 5

Oral Absorption of Different Zinc Compounds

When considering zinc supplements taken orally (rather than topical application), the absorption rates differ significantly by compound:

• Zinc citrate: 61.3% absorption rate
• Zinc gluconate: 60.9% absorption rate
• Zinc oxide: 49.9% absorption rate 6

Some individuals may have minimal absorption from zinc oxide when taken orally without food 6. This makes zinc oxide less effective as an oral supplement compared to more soluble forms like zinc citrate or gluconate.

Clinical Implications

• For sunscreens and topical applications, the minimal absorption of zinc oxide contributes to its excellent safety profile
• For therapeutic zinc supplementation, other forms like zinc gluconate or zinc citrate would be preferable due to their higher bioavailability 6
• When using zinc oxide in sunscreens, there appears to be no significant risk of systemic toxicity due to the minimal absorption 2, 4

Important Considerations

• Taking zinc supplements with food can interfere with zinc absorption and effectiveness of treatment 1
• For optimal absorption of oral zinc supplements, they should be taken on an empty stomach, at least 30 minutes before meals 7
• Avoid taking zinc supplements with foods high in phytates or other mineral supplements, especially iron and calcium, as these can further reduce absorption 7

In conclusion, zinc oxide has minimal systemic absorption when applied topically, making it safe for use in sunscreens and other dermal applications. For oral supplementation, other zinc compounds with higher bioavailability would be more appropriate.