Zinc Oxide
Classic dermatological active ingredient with astringent and wound-healing properties
Zinc oxide (chemical formula ZnO) is an inorganic compound that has been used in medicine and pharmacy for centuries. As a white, powdery mineral, zinc oxide combines several therapeutically valuable properties: it acts as an astringent (constricting), antiseptic, wound-protective, drying agent and as a physical sunscreen filter. In modern dermatology, zinc oxide is widely used in pastes, ointments, creams, powders and medical plasters.
Zinc oxide is an ingredient in numerous over-the-counter products such as wound pastes (e.g. Penaten cream), sunscreens and wound dressings. It is considered one of the best-tolerated dermatological active ingredients and is also suitable for newborns, pregnant women and nursing mothers. In addition to dermatology, zinc oxide is used as a radiation shield in dentistry (zinc oxide-eugenol pastes) and as an additive in medical dressings.
Mechanism of Action
The dermatological effects of zinc oxide are based on several complementary mechanisms. The astringent effect arises from the ability of zinc ions to denature proteins in the uppermost skin layer, thereby creating a protective protein layer that reduces secretions, reduces inflammatory reactions and protects the skin from irritants. This effect explains its use in weeping and irritated skin areas.
The antimicrobial effect of zinc oxide is based on the release of zinc ions (Zn2+), which are antibacterial and antifungal. Zinc ions disrupt cell membrane integrity in microorganisms, inhibit enzymes of cell metabolism and impede cell division. The antimicrobial activity is broad but weaker than with classic antibiotics, which is why zinc oxide is used primarily preventively and in mild infection risks.
As a physical UV filter, zinc oxide reflects and scatters UV radiation in the UVA and UVB range without chemical reaction. Unlike chemical UV filters, zinc oxide acts purely physically and is not absorbed into the skin, making it particularly suitable for sensitive skin and children. Zinc oxide provides broad UV protection from UVB (280 to 315 nm) deep into the UVA range (315 to 400 nm).
At the cellular level, zinc ions promote wound healing by stimulating fibroblast proliferation, collagen synthesis and epidermal regeneration. Zinc is an essential trace element for numerous enzymes, including metalloproteinases, which play a role in tissue remodelling.
Indications
- Nappy rash (diaper dermatitis): Prophylaxis and treatment of skin redness and irritation in the nappy area of infants; zinc oxide paste protects the skin from moisture and irritating substances
- Weeping and irritated skin: Eczemas, intertrigo (skin fold irritation), seborrhoeic dermatitis, perianal and genital dermatitis
- Wound care: Superficial wounds, abrasions, skin lacerations, mild first-degree burns
- Sun protection: Broad UVA/UVB protection in sunscreens, especially for children, newborns, sensitive skin and people with contact allergies to chemical UV filters
- Radiation dermatitis: Prophylaxis and relief of skin irritations in the radiation field during oncological therapy
- Acne: Mild antiseptic and drying effect in acne vulgaris; in combination with other acne ingredients
- Leg ulcers (venous ulcers): Zinc oxide bandages and compression dressings for wound conditioning and skin protection of the wound surroundings
- Dentistry: Zinc oxide-eugenol pastes as temporary filling and wound dressing in endo and paediatric dentistry
Dosage and Application
Pastes and ointments: Apply once to several times daily to the affected area; for nappy rash, apply at every nappy change after cleaning and drying the skin. Zinc oxide paste is usually applied generously as a protective layer, not rubbed in. Baby oil or skin lotion is suitable for removal, as water and soap are not effective at removing the paste.
Wound dressings and bandages: Apply according to medical instructions; zinc oxide compresses are placed on the wound and fixed with dressing material. Change as directed by a physician (usually every 1 to 3 days).
Sunscreens: Apply generously 15 to 30 minutes before going outdoors; reapply regularly, especially after swimming or heavy sweating.
Powder: Dust thinly onto dry, clean skin; especially in skin folds for moisture absorption. Caution: do not use powder in the facial area of infants (risk of aspiration).
Side Effects
Zinc oxide is considered extraordinarily well tolerated. Adverse effects are rare:
Occasionally: Local dryness or mild tension in the skin, especially with frequent application or on already very dry skin. Occasionally zinc oxide in combination with certain excipients (lanolin, fragrances) can trigger contact allergies; allergy to zinc oxide itself is very rare.
With excessive or long-term application to large areas: Systemic zinc absorption is possible but clinically generally insignificant, since percutaneous absorption is very low. Chronic zinc intoxications from topical zinc oxide have not been described.
Sunscreens with nano-zinc oxide: Nanoparticulate zinc oxide has higher transparency on the skin, but there are still discussions about the safety of nanoparticles on mechanically heavily stressed or injured skin. On intact skin, nano-zinc oxide is considered safe according to current scientific assessment.
Interactions
With topical application, no clinically relevant interactions with systemic medications are known, as zinc oxide is barely absorbed.
Locally relevant: zinc oxide can influence the effectiveness of certain simultaneously applied topical active ingredients (e.g. antibiotics, corticosteroids) by forming a barrier layer. With combination applications, attention should therefore be paid to which preparation is applied first and whether occlusion is desired or not.
In dentistry: zinc oxide-eugenol pastes can be cytotoxic with direct pulp contact; their use as direct pulp capping is not recommended.
Special Notes
Pregnancy and breastfeeding: Zinc oxide is classified as safe with topical application and can be used during pregnancy and breastfeeding. Zinc is an essential nutrient; systemic exposure from topical application is negligibly low.
Infants and newborns: Zinc oxide paste is one of the recommended measures for the prophylaxis and treatment of nappy rash in infants. Powders should not be used in the facial area of infants, as the fine particles can be inhaled and cause respiratory problems.
Wound healing: Zinc oxide should not be applied to deeply infected wounds, untreated abscesses or severely necrotic wound areas without simultaneous specific wound treatment by medical professionals.
White discolouration with sunscreens: Conventional (non-nano) zinc oxide leaves a white film on the skin. This does not pose a health problem, but some users find it cosmetically undesirable. New formulations with micronised or nano-scale zinc oxide are more transparent.
Frequently Asked Questions
Is zinc oxide the same as zinc paste?
No, zinc paste is a specific preparation made from zinc oxide (usually 25% zinc oxide) embedded in a paste base of starch and petroleum jelly. Pure zinc oxide paste contains a higher proportion of zinc oxide and a different base. The term zinc paste is commonly used for various zinc-containing preparations; the exact composition should be taken from the respective product.
Does zinc oxide protect against UVA and UVB?
Yes, zinc oxide is one of the few physical sunscreen agents that effectively blocks both UVA and UVB radiation. Compared to titanium dioxide, another physical UV filter, zinc oxide covers the UVA range better and is therefore considered an optimal broad-spectrum protection.
How long can zinc oxide paste be used for nappy rash?
Zinc oxide paste can be used for nappy rash as long as symptoms persist. In mild cases, the situation usually improves within 2 to 3 days. Persistent or worsening redness, blisters or weeping should be medically assessed, as a fungal infection (Candida) or other skin condition may be present.
References
- Federal Institute for Drugs and Medical Devices (BfArM): Monograph Zinc Oxide
- Scientific Committee on Consumer Safety (SCCS): Opinion on Zinc Oxide (nano), 2021
- European Medicines Agency (EMA): Monographs on dermatological active ingredients
- Dronkers TMG et al.: Zinc oxide in wound care. Wound Repair and Regeneration, 2018
- German Dermatological Society (DDG): Guideline Nappy Rash, 2022