Chemistry, Ingredients, and Product Knowledge
Chemistry, Ingredients, and Product Knowledge tests pH, functional ingredient categories, how actives behave inside a formula, and how sunscreen and labeling claims are regulated.
pH and formulation basics
The pH scale runs 0–14 and skin sits near 4.5–5.5. pH changes how an acid behaves: glycolic at pH 3 exfoliates, at pH 5 it barely does. Know the forms: solutions, suspensions, emulsions (oil and water held together by emulsifiers), gels and ointments. Surfactants clean by joining water to oil; nonionic and amphoteric surfactants are gentler than harsh anionics.
Functional categories
- Humectants bind water: glycerin, hyaluronic acid, sorbitol.
- Emollients soften and smooth: plant oils, esters, lanolin.
- Occlusives block water loss: petrolatum, dimethicone, beeswax.
- Preservatives keep water-containing products safe: phenoxyethanol, parabens, benzyl alcohol. Any formula containing water needs a preservative system.
- Antioxidants protect both formula and skin: vitamins C and E, green tea.
Actives worth knowing
L-ascorbic acid is unstable and oxidizes brown; it performs best below pH 3.5 and needs opaque packaging. Retinol converts in skin to retinoic acid, is photosensitive, and is used at night. Niacinamide supports the barrier, peptides signal collagen production, and salicylic acid is lipid-soluble.
Sunscreen and claims
SPF measures UVB protection only; UVA needs a PA or broad-spectrum rating. Organic filters (avobenzone, octinoxate) absorb UV; inorganic filters (zinc oxide, titanium dioxide) scatter it. Reapply every two hours. Under FDA rules, a product that alters skin structure or claims to treat disease is a drug, not a cosmetic - which is why you must never promise to cure a condition.
Worked example
A vitamin C serum has turned dark orange. Reasoning: it has oxidized and lost potency, so discard it rather than reassure the client that the color is normal.
Traps that cost marks
- Judging an acid by percentage alone.
- Believing natural products cannot cause allergy.
- Treating SPF as a UVA rating.
- Layering actives without regard to pH.