Is it harmful to use oxidized vitamin C serum?
                                
                                
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                                    4 min read                                
                            
                                Over 5.3 million Instagram posts use the hashtag #VitaminC, yet many users are unaware of the risks associated with this notoriously unstable ingredient. A serum can lose its potency and potentially cause harm when exposed to air, light, or heat, begging the question: is it harmful to use oxidized vitamin C serum?