Zinc oxide
Zinc oxide
Generic Name
Zinc oxide
Mechanism
- Zinc oxide is a *physical* (mineral) barrier that reflects and scatters ultraviolet (UV) radiation, reducing skin exposure to UVA and UVB rays.
- As a topical *inhibitor* of keratinocyte proliferation, it exhibits mild anti‑inflammatory activity by suppressing prostaglandin synthesis and down‑regulating pro‑inflammatory cytokines.
- In *topical* preparations, it also stabilizes the skin barrier, reduces transepidermal water loss, and promotes wound healing through modulation of growth factor pathways.
Pharmacokinetics
- Absorption: Negligible systemic absorption from intact skin; < 0.5 % reaches circulation.
- Distribution: Primarily remains in the epidermis and superficial dermis.
- Metabolism: Not metabolized; remains particle‑wise as ZnO.
- Excretion: Clearance via renal excretion of trace Zn⁺² in urine; topically applied amounts excreted unchanged through sweat.
- Onset/Duration: Rapid onset (minutes) of UV protection; protection persists until product is removed or degraded.
Indications
- Dermatologic & Ophthalmic
- Sunburn protection (sunscreens, after‑sun care).
- Mild to moderate diaper rash.
- Mechanical irritation (rash, eczema, insect bites).
- Minor burns and cuts to calm inflammation.
- Ocular surface protection (conjunctival shielding) in contact lens use or after surgery.
- Cosmetic
- Skin‑lightening formulations as UV filter.
- Anti‑acne preparations to reduce irritation.
Contraindications
- Allergic reaction to zinc or related metals.
- Use caution in patients with *hypersensitivity* to *copper* or *tin*; cross‑reactivity is rare but possible.
- Avoid ingestion due to potential acute gastrointestinal toxicity; contraindicated for oral ingestion in children under 12 months.
- Pregnancy/Lactation: Generally safe as topical; not contraindicated, but avoid ingestion.
- Post‑operative wounds: Use only as directed; avoid high‑pressure cleaning that could displace the barrier.
Dosing
| Form | Application | Typical Dose | Frequency |
| Topical cream/aquabuffer | Evenly apply thin layer over affected area | 1–2 % weight/volume in base (e.g., 2 g cream) | As needed, up to 2–4 × day |
| Sunscreen lotion | Apply ~2 mg cm⁻² over entire surface | 15–30 % zinc oxide in lotion | Reapply every 2 h (or after swimming/showering) |
| Oral supplement *(rare; high‑dose formulations for deficiency)* | Take with meals | 15–30 mg elemental Zn ⁺² | 1× day |
| Ocular solution | Instill 1–2 drops | 1–2 % ZnO in sterile saline | 2–4 × day |
• *Infant care:* Use *0.5–1 %* zinc oxide cream; apply sparingly to diaper area.
• Do not occlude areas with excessive moisture; ensure proper drying before clothing.
Adverse Effects
| Category | Adverse Effect | Notes |
| Local | Irritant dermatitis (redness, pruritus) | More common in infants or compromised skin. |
| Contact allergy | Rare; treat with topical steroids if persistent. | |
| Coating/trail residue | Can cause temporary skin staining. | |
| Systemic (rare) | Gastrointestinal upset (nausea, vomiting) | Only after oral ingestion or accidental swallowing. |
| Zinc toxicity (hyperzincemia) | Symptoms: metallic taste, headache, tremor, thrombocytopenia. | |
| Serious | Anaphylaxis | Extremely rare; monitor for swelling, difficulty breathing. |
| Hemolysis in G6PD deficiency (when used orally at high dose) | Avoid high dosing in G6PD‑deficient patients. |
Monitoring
- Topical use: Visual inspection for dermatitis; watch for any worsening erythema.
- Oral forms: Serum zinc levels > 120 µg/dL (12 µmol/L) warrants dose reduction; monitor liver transaminases if chronic therapy > 3 months.
- In infants: Ensure no ingestion; monitor weight gain and appetite if used for diaper rash.
Clinical Pearls
- “Invisible Shield” – Zinc oxide remains on the skin surface, providing protection independent of skin penetration; use it as a *backup* for SPF‑deficient sunscreens.
- Dual‑Action – In diaper rash, the anti‑inflammatory effect of ZnO works alongside its physical barrier to reduce the need for steroids.
- Fast‑Acting – Apply immediately after sunburn to reduce pain and inflammation; the protection lasts until wash‑off.
- Patch‑Tested – Always perform a 48‑hour patch test on a small skin area for any new topical product containing zinc oxide.
- Use in Burns – For superficial burns, zinc oxide creams can reduce pain and help prevent infection due to their occlusive, antibacterial properties.
- Ocular Safety – When protecting ocular surfaces (contact lenses, post‑operative care), choose ophthalmic‑grade zinc oxide solutions (1–2 %) over creams to avoid mucous irritation.
- Weight‑Based Dosing for Supplements – Children < 1 year: limit to 5 mg elemental Zn ⁺²/day; older children 8–12 y: 10–15 mg/day, monitored for growth parameters.
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