Which cream is formed by adding a large amount of stearic acid to an O/W emulsion where part of the stearic acid converts to soap by adding a base or neutralizing agent?

• A. Vanishing cream
• B. Cold cream
• C. Creamy ointment
• D. Lubricating lotion

Answer: (A)

Vanishing cream is formed when a large amount of stearic acid is used in an oil-in-water emulsion and part of that acid is converted to soap salts by adding a base. The soap, such as sodium stearate, is a strong emulsifier that is hydrophilic and stabilizes the oil droplets in the aqueous phase. This in situ saponification creates a light, water-washable emulsion with a non-greasy feel, so the cream seems to “vanish” when rubbed with water. That's the defining feature of vanishing cream—the combination of a soap-forming fatty acid in an O/W system yields a smooth, washable, non-sticky product.

The other options describe different product textures and behaviors: a heavier, more oil-rich cream tends to leave a film and is less easily washed off; a creamy ointment is thicker and ointment-like; a lubricating lotion is typically more watery and does not rely on substantial in situ soap formation.