Chemistry, Product Ingredients, and Product Selection
What the exam tests
Product chemistry questions test pH, solubility, ingredient function, preservatives, and matching products to skin needs.
Core rules
- pH scale: lower is more acidic. Skin surface is about pH 4.5–5.5; high-pH cleansers can strip the barrier.
- Surfactants clean by lowering surface tension; humectants attract water; emollients soften; occlusives reduce water loss.
- AHAs and BHAs need an effective pH; BHA is oil-soluble and suited to pores; AHA is water-soluble and suited to surface texture.
- Antioxidants such as vitamin C can oxidize; packaging and expiration matter.
- Preservatives prevent microbial growth; water-containing products need them.
- “Fragrance-free” and “unscented” are not identical; patch test and read labels.
- Product selection considers skin type, sensitivity, allergies, treatment history, and client goals-not trends.
Worked example
A client with sensitive skin and fragrance allergy wants a brightening serum. Reasoning: choose a fragrance-free, low-irritant formula and introduce slowly. Avoid stacking multiple acids. Document the product and patch test.
Traps
Believing “chemical-free”; assuming natural means safe; mixing acids without pH knowledge; and ignoring expiration or contamination.