In the products discussed here, the daytime-versus-nighttime distinction depends on the ingredients inside the product, not simply on whether it is called a cream, serum or toner. Products containing glycolic acid, lactic acid or certain photosensitive essential oils were treated as nighttime products, while daytime versions omitted those components.
Why the product name is not enough
It is tempting to think that a serum is automatically suitable at one time of day and a cream at another. That is not how I make the distinction. Two products with the same general format can have different intended use depending on the active ingredients included in that particular version.
The role of glycolic and lactic acid
Glycolic acid and lactic acid are used for removing dead skin. The reasoning is that accumulated dead skin can make the surface look dull and can interfere with the penetration of beneficial ingredients. At gentle use levels they are intended to provide regular exfoliation, while much higher concentrations are described as capable of burning the skin.
Why nighttime comes into the discussion
In the workshop products, formulas containing glycolic or lactic acid were treated as nighttime versions. The same applies to creams containing photosensitive essential oils such as lemon, orange or bergamot. A daytime version was discussed as one from which these photosensitive components were removed.
A practical layering point
When a serum is used before a cream or moisturizer, it should first be allowed time to absorb rather than immediately covering it with the next product. This is part of thinking about a routine as deliberate layering rather than simply stacking several products on the skin.
The practical takeaway
When deciding whether a skincare product belongs in the morning or evening, look beyond the words ‘serum’, ‘toner’ or ‘cream’. The ingredient profile of that particular product is what determines the day-versus-night distinction in this approach.
Related Guides
- What Is a Korean Skin Polish, and How Is It Different From a Coarse Scrub?
- Toner vs Serum in Korean Skincare: What’s the Difference?
- What Does Hyaluronic Acid Do in Skincare, and Why Does Molecular Weight Matter?
