Combining retinol with Alpha Hydroxy Acids (AHAs) or Beta Hydroxy Acids (BHAs) can result in excessive dehydration, redness, and irritation.
Vitamin C and niacinamide are both excellent constituents for reducing hyperpigmentation and brightening the skin, but they can cancel each other out when used together.
The combination of benzoyl peroxide and retinol can lead to excessive dryness and irritation. These ingredients are both potent.
When combined, vitamin C and retinol can destabilize each other, diminishing their efficacy. Use vitamin C in the morning and retinol at night.
Combining multiple exfoliating acids can erode the skin's natural moisture barrier and cause irritation. Choose one reagent and use it per the instructions.
Using both chemical and physical exfoliants in the same regimen can result in over-exfoliation and damage to the skin's protective barrier.
Copper peptides can inhibit the effectiveness of niacinamide, so it is best to avoid using them together.
Combining diverse forms of vitamin A, such as retinol and other retinoids, can irritate and sensitize the skin. Stick to one vitamin A derivative at a time.
Strong acids, such as glycolic acid or salicylic acid, destabilize and diminish the efficacy of vitamin C. Utilize vitamin C in the morning and acids in the evening.
Using too many active ingredients at once can overwhelm and irritate the epidermis. Start with one or two active ingredients.