Chemistry, Products, and Makeup
Chemistry, Products, and Makeup
This domain tests the chemistry behind the shelf: pH, emulsions, functional ingredients, regulatory classification, and the color work that finishes a service.
pH and emulsions
pH runs 0–14, and skin sits near 4.5–5.5. Alpha hydroxy acids need free acid at low pH (glycolic and lactic typically around pH 3–4) to exfoliate; adding a base neutralizes them. Salicylic acid, a BHA, is oil-soluble and works inside the pore. An emulsion is oil and water held together by an emulsifier: oil-in-water lotions feel light and non-greasy, while water-in-oil creams are richer and more occlusive.
Functional categories
Humectants (glycerin, hyaluronic acid, urea) draw water in. Emollients (shea butter, squalane, fatty alcohols) soften and fill the spaces between corneocytes. Occlusives (petrolatum, dimethicone) block water loss. Antioxidants (L-ascorbic acid, tocopherol, ferulic acid) neutralize free radicals; L-ascorbic acid is unstable above about pH 3.5 and oxidizes to yellow-brown. Retinoids speed cell turnover and increase photosensitivity.
Cosmetic versus drug
A product that cleanses, beautifies, or alters appearance is a cosmetic. One that affects structure or function, or makes a therapeutic claim (sunscreen, acne treatment, barrier repair), is a drug and needs an approved active and compliant labeling. "Hypoallergenic," "natural," and "organic" are marketing terms without a standard definition.
Color correction
Green neutralizes redness; peach or orange cancels blue-purple under-eye circles; lavender lifts sallow yellow tones; yellow cancels purple bruising. Match foundation to undertone - warm, cool, or neutral - at the jawline in daylight, not to the depth of the hand.
Worked example
A serum labeled "20% vitamin C" arrives brown and smells sharp. Reasoning: L-ascorbic acid has oxidized, so the active is degraded and the color confirms it. Do not use it on a client and do not promise results; replace it and store the new bottle away from light and heat.
Traps that cost marks
Assuming a higher percentage is stronger without checking pH. Layering an AHA and a retinoid in one session for a first-time client. Sharing mascara or lip products, or double-dipping into cream jars. Presenting "medical grade" or "clinical" as a regulated standard when it is not.