Chemistry and Product Knowledge
What the exam tests
Chemistry questions ask about pH, acids and bases, ingredient function, product formulation, and incompatibilities. You need to explain why a product works and when it is unsafe.
Core concepts
- pH scale 0–14; skin surface is about pH 4.5–5.5. Lower pH is more acidic; higher pH is more alkaline. Alkaline cleansers can strip the barrier.
- AHAs such as glycolic, lactic, and mandelic are water-soluble; BHAs such as salicylic acid are oil-soluble and useful in pores. Efficacy depends on concentration, pH, and free-acid availability.
- Enzymes such as papain and bromelain digest keratin; they are gentler but can still irritate.
- Function categories: humectants such as glycerin and hyaluronic acid draw water; emollients such as oils and esters soften; occlusives such as petrolatum and dimethicone block water loss; surfactants cleanse; emulsifiers blend oil and water; preservatives prevent microbes; antioxidants stabilize formulas.
- Label order lists ingredients by weight down to 1 percent; fragrance and parfum can hide allergens.
- Incompatibilities: retinoids plus strong acids can over-irritate; vitamin C plus benzoyl peroxide can oxidize; do not mix professional peels without training.
Worked example
A client wants a 10 percent glycolic product but her skin stings. Reasoning: 10 percent at pH 3.5 has more free acid than 10 percent at pH 4.5; concentration alone is not the whole story. Start lower and less frequent, support the barrier, and screen for retinoid use.
Traps
- Assuming natural means non-irritating.
- Ignoring pH when comparing acids.
- Mixing actives without checking stability.
- Using expired or improperly stored vitamin C.