Zinc Oxide – Effects, Uses and Safety

What is Zinc Oxide?

Zinc oxide (chemical formula: ZnO) is an inorganic compound composed of zinc and oxygen. It appears as a fine white powder and is nearly insoluble in water. Zinc oxide has been used in medicine and pharmacy for centuries and is considered one of the oldest known remedies for skin and wound treatment. Today, it is found in dermatological products, sunscreens, toothpastes, medical dressings, and dietary supplements.

Mechanism of Action

Zinc oxide exerts its effects through several mechanisms:

• Astringent effect: It mildly tightens the skin, reduces secretion, and has anti-inflammatory properties.
• Antiseptic effect: Zinc ions inhibit the growth of bacteria and fungi on the skin surface.
• Barrier protection: As a physical UV filter, zinc oxide reflects and scatters both UVA and UVB radiation without absorbing it.
• Wound healing: Zinc is an essential cofactor for numerous enzymes involved in cell regeneration and tissue repair.

Medical Applications

Dermatology and Wound Care

Zinc oxide is widely used in ointments, creams, and pastes to treat wounds, skin irritations, eczema, diaper rash, and to relieve itching. Zinc oxide paste is a classic remedy for inflammatory skin conditions and the care of sensitive or irritated skin.

Sun Protection

As a physical UV filter, zinc oxide is a key ingredient in sunscreens. Unlike chemical UV filters, it works mechanically by reflecting and scattering UV light without being absorbed through the skin. It provides broad-spectrum protection against UVA and UVB radiation and is considered particularly well-tolerated, even for children and sensitive skin types.

Dentistry

In dentistry, zinc oxide is combined with eugenol to form a temporary filling or base material (zinc oxide-eugenol cement). This combination has antimicrobial properties and provides mild analgesic (pain-relieving) effects.

Dietary Supplementation

As a source of bioavailable zinc, zinc oxide can be used in dietary supplements, although other zinc compounds (e.g., zinc gluconate, zinc citrate) are generally considered to have higher bioavailability. Zinc itself is essential for immune function, wound healing, hormone metabolism, and cognitive performance.

Dosage and Usage

The concentration of zinc oxide in skincare products typically ranges from 5% to 40%, depending on the intended use. Sunscreens commonly contain 10–25% zinc oxide. As an oral supplement, zinc oxide is used in amounts corresponding to the daily zinc requirement (recommended daily intake according to EFSA: 7–16 mg for adults).

Safety and Side Effects

Zinc oxide is considered very well-tolerated and safe for topical use. Adverse effects are rare and may include:

• Mild skin redness or irritation in very sensitive individuals
• A whitish residue on the skin at high concentrations (particularly in sunscreens)

Inhalation of zinc oxide dust or fumes (e.g., in industrial settings) can cause so-called metal fume fever, presenting with flu-like symptoms. However, this is not relevant for the normal use of cosmetics or medical products.

Nanoparticle zinc oxide, used in some sunscreens, is currently under discussion regarding safety and potential deep skin penetration. Current scientific evidence, however, shows no significant penetration through intact skin.

Interactions

When taken orally, zinc oxide may reduce the absorption of certain antibiotics (e.g., tetracyclines, fluoroquinolones) and iron. A time interval of at least 2 hours between intake is recommended.

References

1. European Food Safety Authority (EFSA): Dietary Reference Values for Zinc. EFSA Journal, 2014.
2. Pinnell SR et al. - Microfine Zinc Oxide is a Superior Sunscreen Ingredient to Microfine Titanium Dioxide. Dermatologic Surgery, 2000.
3. Lansdown AB et al. - Zinc in wound healing: Theoretical, experimental, and clinical aspects. Wound Repair and Regeneration, 2007.