Rather a lot, as it happens. At their best, serums deliver a concentrated hit of active ingredients into parts of your skin that moisturisers can’t quite reach and they leave your complexion soft and beautifully prepped for moisturiser.

‘The molecular structure of serum gives it much more penetration so the availability of active ingredients is increased, making serums brilliant for targeting specific problems, like wrinkles, pigmentation or dehydration,’ says leading London-based facialist Anastasia Achilleos.

‘They also prime skin for moisturiser, which works in tandem with serum to provide a protective, hydrating barrier.’

Certainly, all the derms and skin care specialists I’ve spoken to agree that a well-chosen serum plus moisturiser is the ideal treatment for skin, and I’ve found it works brilliantly on mine.

Most also advise applying your serum to slightly damp skin – it gives a better glide and helps it sink in better. And give it a minute or so before adding moisturiser.

Here are five of my favourite serums:

Vitamin A&C Serum, £84, by Lisa Hoffman

Great for dry skin, this silky, luxurious serum is seriously nourishing and leaves skin instantly softer. Use this and skip moisturiser in the morning when the weather gets too warm for layers of product.

Advanced Luminescence Serum, £85, by Zelens

This gorgeously-scented serum is a make-up artist’s favourite with good reason: it glides beautifully in to skin and makes it look luminous straight away. It works long-term, too – I started getting compliments on my skin within two weeks of using it, and I know another beauty editor who says it's the only thing she puts on her skin at night.

Regenerist Daily Regenerating Serum, £22.50, by Olay

Loaded with amino-peptides – said to help regenerate skin cells – this is a good, general-purpose serum that absorbs really well and helps skin look brighter.

Vital Essence, £67.53, by Chantecaille.

A light, non-greasy serum that balances and brightens oily complexions beautifully. Try it on combination skin for summer.

Lagoon Serum, £52, by Carita

Use this hydrating, mineral-rich serum under a face oil at night to bring parched skin back to life. Ideal for post-sunbathing repair.

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