Product knowledge, chemistry and ingredient awareness
Product knowledge, chemistry and ingredient awareness
This domain tests basic cosmetic chemistry: pH, surfactants, emulsifiers, humectants, emollients, preservatives, actives and labelling, and how these affect product choice and safety.
Core rules
- pH measures acidity and alkalinity from 0 to 14. Skin is about pH 4.5 to 5.5; alpha-hydroxy acids need low pH, around 3 to 4, to exfoliate.
- Surfactants clean by suspending oil and dirt; they can be anionic, cationic, amphoteric or non-ionic. Harsh surfactants can strip the barrier.
- Emulsifiers hold oil and water together; humectants attract water (glycerin, hyaluronic acid); emollients soften (oils, esters); occlusives seal (petrolatum, dimethicone).
- Preservatives prevent microbial growth; parabens, phenoxyethanol and others are used at regulated levels. Preservative-free products need careful packaging and short shelf life.
- Actives include retinol, vitamin C, niacinamide, AHAs and salicylic acid. They can irritate; introduce gradually and avoid incompatible combinations.
- INCI lists ingredients in descending order up to 1%; allergens must be declared. Check PAO, the period after opening, and storage.
- Patch test new products, especially on sensitive clients.
Worked example
A client wants to use a 10% glycolic toner and a retinol serum nightly. The reasoning is that both increase cell turnover and barrier stress. Recommend alternating nights, a low-strength start, daily SPF and a bland moisturiser, and stop if irritation occurs.
Traps
Equating natural with safe; believing chemical-free is meaningful; mixing acids and retinol immediately; ignoring the PAO symbol.