Skin Care Products, Ingredients, and Basic Chemistry
Basic chemistry you need
Products are solutions, suspensions, or emulsions (oil and water held together by an emulsifier). Surfactants lift oil and debris; humectants (glycerin, hyaluronic acid) attract water; emollients soften; occlusives (petrolatum, dimethicone) seal. The pH scale runs 0–14, with skin near 4.5–5.5 - acids below that range exfoliate more aggressively.
Ingredient families
Alpha hydroxy acids (glycolic, lactic) exfoliate and need an acidic pH to work; beta hydroxy acid (salicylic) is oil-soluble and suited to congestion; vitamin C (L-ascorbic acid) is an antioxidant that oxidizes with light and air; niacinamide supports barrier and tone; retinoids accelerate cell turnover and cause photosensitivity and irritation - no waxing during use; benzoyl peroxide is antibacterial and drying; hydroquinone is a drug used for pigmentation. Sunscreens are physical (zinc oxide, titanium dioxide) or chemical filters and should be broad spectrum, SPF 30 or higher.
Reading the label
Ingredients are listed in descending order of concentration up to one percent; below that, order is flexible. "Hypoallergenic," "noncomedogenic," "clean," and "dermatologist-tested" are marketing terms without legal definition, while drug claims (treats acne, changes pigment) put a product in a different regulatory class.
Rule of thumb: patch test every new product and never combine strong exfoliants, retinoids, and waxing in the same visit.