Chemistry, Product Ingredients, and Product Selection
Functional chemistry
Products are systems: water, surfactants, humectants, emollients, occlusives, actives, preservatives, and fragrance. Surfactants lift oil; humectants bind water; emollients soften; occlusives slow water loss. Emulsions combine oil and water with emulsifiers. pH matters. AHAs need an effective free-acid level, and the acid mantle sits mildly acidic. Preservatives prevent microbial growth; a natural product is not automatically safer.
Actives and selection
- AHAs such as glycolic and lactic acid exfoliate superficially; BHA, salicylic acid, is oil-soluble and suited to oily pores.
- Retinoids increase turnover and photosensitivity; warn about irritation.
- Vitamin C is an antioxidant but oxidizes; packaging matters.
- Niacinamide supports barrier and tone; benzoyl peroxide is antibacterial and drying.
- Fragrance and essential oils are common sensitizers.
Worked example
A client using benzoyl peroxide wants to add vitamin C. Reasoning: the combination can oxidize and irritate, and both can be drying. Better to alternate: benzoyl peroxide at night, vitamin C in the morning, and introduce one at a time with SPF. Do not layer incompatible actives just because the labels sound complementary.
Traps
- Chemical-free marketing. Water is a chemical.
- Assuming a higher percentage always gives better results.
- Ignoring pH and contact time.
- Mixing too many actives at once.
- Forgetting preservative and contamination risk.
Exam lens
Match the ingredient mechanism to the client's finding and barrier tolerance.