Chemistry, Products, and Product Selection
pH and the acid mantle
Skin's surface sits slightly acidic (roughly pH 4.5–5.5). Products far outside that range disrupt the barrier. pH scale runs 0–14; lower is acidic, higher is alkaline. Understanding pH explains why alkaline soaps feel stripping and why acids exfoliate. Buffers resist pH change; surfactants lift oil and debris.
Key ingredient families
- Humectants (glycerin, hyaluronic acid) attract water.
- Emollients (oils, esters) soften and smooth.
- Occlusives (petrolatum, dimethicone) seal in moisture.
- Antioxidants (vitamin C, E) neutralize free radicals.
- Exfoliants - AHAs (water-soluble, surface) and BHAs (oil-soluble, pore-penetrating).
- Sunscreens - physical (zinc oxide, titanium dioxide) vs. chemical filters.
Emulsions and product forms
An emulsion combines oil and water with an emulsifier; oil-in-water is lighter, water-in-oil is richer. Serums are lightweight and penetrate; creams are heavier and seal. Preservatives are necessary in any water-containing product.
Traps
- "Natural" equals safe - false; botanicals cause contact dermatitis.
- Higher percentage always better - false; irritation risk rises.
- Mixing actives - layering strong acids with retinoids over-irritates.
- Confusing humectant and occlusive - one attracts water, the other blocks loss.
Worked example
A client with dry, dehydrated skin: recommend a humectant serum (glycerin/hyaluronic acid) under an occlusive moisturizer, plus SPF. The humectant draws water; the occlusive holds it in.