Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder which is insoluble in water. ZnO crystallizes primarily in the hexagonal wurtzite structure at ambient conditions and exhibits a wide direct band gap of about 3.3 eV and a large exciton binding energy near 60 meV, giving it useful optical and electronic properties. It is an intrinsically n type semiconductor due to native defects such as oxygen vacancies and zinc interstitials. Physical properties include a density of about 5.6 g cm-3, melting point near 1975 C, and good thermal and chemical stability in neutral environments; it dissolves in strong acids and strong bases. Particle morphology ranges from nano to micron scale; surface area, particle size distribution and surface chemistry strongly influence performance in pigments, UV absorbers, ceramics, varistors, rubber vulcanization, and pharmaceutical formulations.
Commercial and laboratory grades of ZnO vary by intended use; typical technical grades contain 98.0 to 99.9 percent ZnO by weight while electronic and reagent grades exceed 99.99 percent. Typical impurity levels for industrial ZnO are in the ppm to low percent range and depend on feedstock and processing. Representative ranges are: iron 10 to 300 ppm, copper 1 to 100 ppm, manganese 1 to 50 ppm, lead less than 10 ppm for many grades and less than 2 ppm for cosmetic grade, cadmium below 1 to 5 ppm, silicon dioxide 0.01 to 0.5 percent, alumina 0.01 to 0.2 percent, alkali metal oxides (Na2O, K2O) combined below 0.1 percent, chloride and sulfate typically below 100 ppm. High purity ZnO for electronics is specified in ppb to single ppm levels for most metallic contaminants. Related zinc compounds that can be present as surface or processing residues include zinc hydroxide Zn(OH)2, basic zinc carbonates such as ZnCO3 or hydrozincite, zinc sulfide ZnS, zinc chloride ZnCl2 and zinc sulfate ZnSO4; moisture and trace organics may also be controlled to low levels depending on grade.
Topical zinc oxide is widely considered safe for skin when formulated at appropriate concentrations and using cosmetic or pharmaceutical grade material. It is a common active ingredient in sunscreens and barrier creams because it blocks UVA and UVB radiation and provides a physical protective layer. Cosmetic grade ZnO is processed to limit toxic metal impurities such as lead and cadmium; those impurity limits are important for skin products. People with specific allergies or very sensitive skin should patch test new products and consult a dermatologist.
Five common uses for zinc oxide are: 1) UV absorber and physical sunscreen active in personal care products, 2) activator and filler in rubber vulcanization for tires and elastomers, 3) white pigment and opacifier in paints, coatings and inks, 4) raw material for ceramics, varistors and electronic components where its semiconducting and piezoelectric properties are used, and 5) pharmaceutical and topical formulations such as diaper rash creams, antiseptic ointments and wound dressings.
Zinc oxide is not a vitamin. Zinc is an essential mineral required for many biological functions, and several zinc compounds are used as dietary supplements. ZnO has relatively low water solubility and therefore lower apparent bioavailability compared with more soluble zinc salts such as zinc sulfate or zinc gluconate. For oral supplementation clinicians and manufacturers often choose more soluble zinc forms; ZnO can be used as a zinc source in some supplements but bioavailability and dose form should be considered.
Zinc oxide can support acne management by providing anti-inflammatory effects, reducing irritation and creating a protective barrier that limits transepidermal water loss. It also has mild antimicrobial activity and can help reduce redness and soothe inflamed lesions. However, it is not a primary prescription acne agent for moderate to severe inflammatory acne; it is often used as an adjunct in over the counter formulations or combined with other actives. Individuals with oily or acne-prone skin should choose non comedogenic formulations and consult a dermatologist for targeted therapy when needed.
