Ointment vs Cream vs Gel

An ointment is a semisolid with an oleaginous or water-free base, such as petrolatum, that stays on the skin and is occlusive. A cream is a semisolid emulsion of oil and water phases, either oil-in-water or water-in-oil, that spreads easily and usually rubs in. A gel is a semisolid in which a liquid, often water or alcohol, is held in a three-dimensional network formed by a gelling agent such as a carbomer or cellulose derivative.

A classification scheme published by FDA scientists (Buhse et al., International Journal of Pharmaceutics, 2005) separates them by measurable properties: water plus volatiles (measured as loss on drying) and composition separate ointments from creams, composition and thermal behaviour separate gels from the other forms, and rheology separates creams from lotions. USP general chapter <1151> describes pharmaceutical dosage forms, and FDA's structured product labelling uses defined dosage-form terms.

On the production floor each form changes the batch record. Creams need separately prepared phases, controlled temperatures, an order of addition and homogenisation before cooling. Ointments need the base melted and the active dispersed or dissolved without settling. Gels need the gelling agent hydrated, often neutralised, and air kept out. In-process checks such as appearance, pH where relevant, viscosity and content uniformity, hold times before filling, and fill-weight checks differ by form.

Whether a cream or gel is a drug, a cosmetic or both depends on its intended use, not its form. A moisturiser making only cosmetic claims is a cosmetic; a product intended to treat acne or protect skin is a drug; and some products are both. OTC drugs may be marketed under the OTC monograph framework in FD&C Act section 505G where the applicable conditions are met.

Related concepts: bulk-to-pack traceability, OTC monograph, MoCRA and hold-time study. Sources: FDA: is it a cosmetic, a drug, or both?, FDA OTC monograph reform, Buhse et al. 2005.