Which thickener is commonly used to prepare gels in topical formulations?

• A. Glycerin
• B. Isopropyl palmitate
• C. Carbomer
• D. Petrolatum

Answer: (C)

In gel-forming topical products, you need a substance that creates a solid-like three-dimensional network within the aqueous phase. Carbomer is a high-molecular-weight polyacrylic acid polymer that swells extensively in water to form a cohesive gel. When the dispersion is neutralized (for example with a base), the polymer chains expand further and the electrostatic repulsion between ionized groups strengthens the gel structure, giving a smooth, clear, and easily spreadable gel that can uniformly suspend actives. This combination of water-swelling and controllable viscosity makes carbomer the standard thickener for topical gels.

Glycerin acts mainly as a humectant and can raise viscosity modestly but does not establish the gel network by itself. Isopropyl palmitate is an oil-like emollient, not a gelling agent, and petrolatum is an occlusive, oil-based base used in ointments/pastes, not for forming aqueous gels.