The difference between a paste and an ointment is, pharmaceutically speaking, only a gradual one. The former contains more solid substances, which makes it thick. Generally speaking, pastes are mixtures of powders with fats. They are usually credited with some absorptive power, and their usefulness in dermatology is partly attributed to this action. Lassar,1 who in 1883 introduced pastes into dermatotherapy, praised them for their porosity. While fats are impermeable to serum or water, he argued, the paste, because of the capillary action of its solid constituents, is capable of taking up serum, which will penetrate the applied layer of the paste and, reaching the surface, will be evaporated. This theory, although appealing, can no longer be accepted.
Before this controversial matter is discussed the original formula of zinc paste and later attempted improvements will be given. Lassar's original formula was as follows:
Salicylic acid .......... 2 Petrolatum .......... 50 Zinc
STRAKOSCH EA. STUDIES ON OINTMENTS: VII. ZINC OXIDE PASTES. Arch Derm Syphilol. 1944;49(1):8–11. doi:10.1001/archderm.1944.01510070011002
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