When should I use a skincare acid?
Both AHAs and BHAs can be used day or night. Some products are formulated to be used at night as an overnight peel, while others (often serums) are meant to be used in the morning to gently slough off any dead skin cells. No matter when you use your skincare acid, always wear proper sun protection during the day—acids can make your skin more sensitive to sunlight.
How much AHA is needed?
As a rule of thumb, the FDA recommends AHA products with an overall AHA concentration of less than 10 percent. This helps prevent side effects from AHAs. Daily use products — such as serum, toners, and moisturizers — contain lower AHA concentrations. For example, a serum or a toner might have a 5 percent AHA concentration.
Can niacinamide and vitamin c be used together?
Some research done in the 1960s showed a negative interaction and that the two could potentially react to produce nicotinic acid, which can cause redness and itching in the skin. But later studies found that it occurred when using pure ascorbic acid and niacinamide held at high temperatures. It's unlikely to be a problem in modern day formulations stored at room temperature. This means that you're safe to use both niacinamide and vitamin C, either together in the same product, or combined from different products that you layer one over the other.