Chemistry, Ingredients, and Product Selection
What the exam tests
This domain tests basic chemistry vocabulary, pH, formulations, and ingredient function so you can select products and explain effects without making medical claims.
Core concepts
- pH measures hydrogen ion concentration; lower pH is more acidic. Skin-friendly formulas are often near pH 4.5 to 5.5.
- Solutions, suspensions, and emulsions differ: an emulsion combines oil and water with an emulsifier.
- Surfactants cleanse by attracting oil and water; they can also disrupt barrier lipids if harsh.
- Humectants attract water, emollients soften, and occlusives reduce water loss.
- Alpha hydroxy acids include glycolic and lactic acid; beta hydroxy acid is salicylic acid. Efficacy depends on concentration, pH, and free-acid availability.
- Antioxidants such as vitamin C can oxidize; packaging and stabilization matter.
Worked example
A client wants a stronger exfoliation and asks whether a 10 percent glycolic product at pH 4.5 is stronger than an 8 percent product at pH 3.5. Reasoning: the lower-pH product likely delivers more free acid and greater exfoliation, even at a lower percentage. Percentage alone is not the whole story; pH and formulation change potency and irritation risk.
Traps that cost marks
Equating a higher percentage with a stronger effect regardless of pH; assuming natural ingredients cannot irritate; mixing incompatible actives such as strong acids with retinoids; and claiming a cosmetic product treats disease.