The product's guidance explicitly states to avoid combining it with other strong actives—such as retinoids or additional exfoliating acids—in the same application, unless you already know your skin tolerates that combination. This is crucial advice. Both retinoids (like retinol) and lactic acid accelerate skin cell turnover and can compromise the skin barrier if used together without proper acclimatization, leading to significant dryness, redness, peeling, and irritation.
A safe strategy is to use them on alternating nights. For example, you might use the lactic acid peeling on Monday and Thursday evenings, and your retinol or vitamin C serum on Tuesday and Friday evenings. This gives your skin a recovery night between active treatments. It is also perfectly acceptable to use this peeling as a temporary replacement for your other actives 1-2 times a week. If you choose to layer products, the lactic acid peeling should be applied to clean, dry skin first, followed after rinsing by a moisturizer. Your retinol or vitamin C serum would then be used on a different night in its own routine. Always introduce one new active at a time and wait at least two weeks before adding another to clearly identify what your skin is reacting to. Consulting a dermatologist or skincare specialist is recommended if you have chronic skin conditions, are pregnant or breastfeeding, or are taking medication that affects skin sensitivity.