It's the product that delivers the highest concentration of actives to your skin, yet serum is still often overlooked in favour of the usual cleanse, tone, moisturise routine - and that's a big mistake.
Generally a thinner consistency than face cream, serum should be applied morning and night after cleansing - however it's not a substitute for a moisturiser, so you'll need to follow up with your usual day or night cream.
While most serums do have moisture-boosting properties, their main aim is to super-charge skin with potent ingredients that target specific complexion concerns.
And right now a flood of innovative formulations have hit the beauty counters, so there's never been a better time to plug that gap in your daily regime - or discover a new favourite.
Take your pick of the best new complexion-improvers.
If defying gravity is top of your beauty wishlist, make a beeline for Clarins Super Restorative Remodelling Serum, £80 (www.clarins.co.uk) which uses extracts from the harungana 'healing tree' of Madagascar to target fibroblasts, the cells where the loosening of the skin happens as we get older, most noticeably around the jawline.
Likewise, Eisenberg Face Refining Serum, £71 (Boots.com) has shown remarkable results in clinical tests, significantly reducing the appearance of a double chin when used daily for two months.
THE VOLUME ADJUSTERS
While losing excess weight is beneficial for health, in terms of your skin condition, a bit of fat is no bad thing. That's why Neroli Firming Intense Facial Serum, £14.99 (www.superfacialist.co.uk) uses apple stem cell technology and hibiscus extract to stimulate lipids and prevent the loss of skin volume.
Argan+ Argan Oil Radiance Lifting Serum, £15.99 (www.feelunique.com) blends five essential oils with so-called "nature's botox" bee venom, at once calming and plumping the skin.
Bee Good's products also harness the power of the hive: Youth Enhancing Hydrate, Smooth & Prime Serum, £25 (www.beegood.co.uk) combines antioxidant-rich honey and propolis (a sticky substance bees use to build) with rich oils and peptides, to boost collagen and tackle wrinkles.
Givenchy's latest high-tech offering, Vax'In City Skin Solution Youth Protecting D-Tox Face Serum, £63.50 (www.feelunique.com) is specially designed to combat the pollution that urbanites are pelted with everyday, keeping wrinkle-free skin smooth (if age is on your side) and slowing the process if it's not.
THE THIRST QUENCHERS
Hydrating serums differ from moisturisers in that they contain ingredients that will draw more moisture into your skin cells, so you'll need to make sure you drink plenty of water too.
Vichy Aqualia Thermal Dynamic Hydration Serum, £22.50 (Boots.com) features a high concentration of moisture-loving hyaluronic acid, as does Filorga Hydra-Hyal Intensive Hydration Plumping Concentrate, £45 (Marksandspencer.com), while Monu Hydra Lift Serum, £29.95 (www.monuskin.co.uk) has added vitamin C and protects against UV damage.
THE REPAIR WORKERS
If you're feeling a little withered and it's showing in your skin, seek out a serum that gets to work beneath the surface to repair from within.
Origins creamy Three Part Harmony Serum, £60 (www.origins.co.uk) is packed with Crambe oil and seed butter, to nourish and hydrate, while the Hydrating Milky Serum, £26 (www.pixibeauty.co.uk) melds jojoba oil and aloe vera to deliver heaps of nutrients where they're needed most.
For oily complexions, try Dr Hauschka's oil-free Night Serum, £39 (www.dr.hauschka.com), which contains apple blossom and witch hazel extracts that help with skin's essential maintenance overnight, without clogging pores.
To deliver a major dose of radiance (without the help of sunshine or spotlights), try Bakel's supremely potent Thio-C Revitalizing Glowing Serum, £118 (www.lookfantastic.com). Each individual vial comes with a lid that dispenses pure vitamin C into a mix of five other antioxidant and emollient ingredients, and must be used within three days before the vitamin is oxidated.
By Terry Cellularose Brightening Serum, £75 (www.uk.spacenk.com) harnesses the brightening properties of white rose cells, the exfoliating effects of flower acids and targets dark spots too, leaving you with a clearer complexion.