Face serum - what is it meant to do?

[ridinghighinapril]

I started using Una Brennan vit C and salycylic acid face wash about 6 monthsago and noticed an almost immediate improvement in my skin. I then started using her serum twice daily about 3 months ago and not sure if there is any difference. My skin is definitely not worse for it but not better either. What is it that serum is actually meant to do??

A serum will usually contain ingredients to address skin issues (blemishes, anti-ageing, redness, dehydration, etc.) in a formula designed to penetrate the skin, rather than in a moisturiser which sits on top of the skin and maybe just sinks in a bit. Which serum is it (I think she does more than one)?

Thanks, Nabootique - it's the vitamin C+ brighten (glow boost skin serum) - not convinced my glow has been boosted!