Does the color change of skin care products mean that they have deteriorated?
No!
Skin care products typically contain active ingredients, some of which are less stable.
It is easy to be changed by the external environment. For example, some whitening ingredients will make the product slightly yellow after oxidation, but this is not deterioration, but some of the active ingredients are partially invalid.
However, if the color of the skin care product changes greatly, and there are black and gray spots, or even the smell changes, it is generally deteriorated and should be discontinued.