The only four skincare ingredients that have been proven to work

This article is part of a special issue investigating key questions about skincare. Find the full series here.

Whether you want to brighten, firm, plump or smooth, there is an eye cream, neck cream, lip cream, face cream, serum, lotion or capsule available, for day or night use. But should you choose the one containing retinol or ceramide; enriched with green tea extract, marine collagen or pentapeptides? The choice of products, ingredients and regimes can be bewildering.

One thing that many dermatologists agree on is that it pays to keep things simple. “If you don’t have time for anything else, a cleanser, moisturiser and sunscreen will cover about 90 per cent of what skin needs on a day-to-day basis,” says Victoria Fu, a skincare chemist and co-founder of Chemist Confessions, a cosmetics company that says it helps consumers decipher skincare ingredients.

Although it is a good idea to cleanse twice a day, doing so in the evening is more important in order to remove the build-up of sweat, oil, pollutants, sun cream and make-up, if you wear it. “The breakdown of those chemicals can cause a stress response in the skin, so it is important to get those things off,” says Emma Craythorne, a London-based dermatologist and founder of skincare company Klira. “It is also important because our skin cells [are constantly replaced], otherwise you end up with bits of dead skin stuck to you like a crusty scale.”

Expensive cleansers aren’t necessary – a soap-free synthetic detergent, such as a gentle cream cleanser, will do, says Craythorne.

Cleansers and moisturisers

After cleansing, most people will want to restore the skin’s protective barrier by applying a moisturiser. A good one will contain three components: an emollient to soften the skin, a humectant to draw water in and an occlusive to prevent moisture escaping. Most brands don’t provide this information on their ingredient lists, but there are websites, such as incidecoder.com, that do. You can also look out for some of the common ingredients that serve these purposes: glycerin and hyaluronic acid are humectants, ceramides and paraffin are emollients, while petroleum jelly and most oils and butters are occlusives. To slow skin ageing and reduce the risk of hyperpigmentation, in which some patches of skin darken, you should also apply some SPF (see Should you really wear sunscreen all year round, even in winter?).

Beyond these basics are active ingredients targeting specific skin concerns, including dullness, uneven texture and signs of ageing.

Deciphering claims about these ingredients can be tricky. “Every year, there are at least three more ‘miracles’ on the market,” says Fu’s colleague and fellow chemist Gloria Wu. However, in their book, Skincare Decoded, they focus on the “big 4” – ingredients with the strongest evidence to back up marketing claims. These are retinoids, vitamin C, niacinamide and alpha hydroxy acids (AHAs).

Whereas ingredients such as hyaluronic acid temporarily plump and smooth the skin, some of the big 4 may have longer-term health benefits. “Retinoids, for example, stimulate collagen production and encourage cellular turnover, which can improve skin resilience, while vitamin C protects the skin from oxidative damage due to environmental stressors like UV exposure and pollution, thus supporting long-term skin health and reducing future damage,” says Anjali Mahto, author of The Skincare Bible and a consultant dermatologist at Self London, a private clinic.

Vitamin variants

Retinoids include a form of vitamin A called all-trans retinoic acid (tretinoin), which is a prescription-only medicine. This is the only cosmetic ingredient for which claims of reductions in wrinkles, sallowness and hyperpigmentation are supported by evidence from randomised clinical trials, the gold standard approach for medical matters, rather than lab-based studies or small, poorly controlled trials. However, tretinoin takes three to six months of regular use to work and can cause skin peeling and irritation, so isn’t suitable for everyone. Gentler alternatives include retinal and retinol, which are converted into retinoic acid in the skin and tend to be less irritating.

Vitamin C also has variants, but most clinical studies have looked at the standard form, L-ascorbic acid. Not only does it neutralise damaging free radical molecules, including ROS, it has also been shown to reduce uneven pigmentation, brightening the skin. L-ascorbic acid is unstable in water, light and air, so products containing it should be kept in a dark cupboard and not stored for too long. It may also irritate sensitive skin, making vitamin C derivatives such as sodium ascorbyl phosphate or ascorbyl glucoside a better option for some.

Then there is niacinamide. Like vitamin C, it has brightening properties and may help to regulate oil production. It may also strengthen the skin’s ability to act as a barrier, reduce inflammation and improve our outer layer’s natural defences over time, says Mahto. However, the evidence for these benefits is weaker than that for vitamin C or retinoic acid.

The final class of ingredient in Fu and Wu’s “big 4” are AHAs. These acids don’t necessarily improve skin health, but by increasing the rate of skin turnover and shedding, they may improve its appearance. “The rate at which these dead cells shed can really slow down with age, and when AHAs have been clinically tested at higher levels, they’ve been found to diminish the looks of fine lines and pigmentation,” says Wu.

Do collagen creams work?

A lot of products also boast about containing collagen, but when you apply this to your skin, it largely functions as another moisturising agent, rather than boosting levels of this structural protein. “It is a humectant, so it can help to keep skin hydrated, but collagen is a really big molecule, so for the most part, it doesn’t really replenish your collagen like the [labels] suggest,” says Wu.

Tempting as it may be to search for a single product that contains multiple active ingredients, this is unwise. “Each of these molecules has their quirks, and trying to formulate all these together wouldn’t be ideal for some of them. For example, ascorbic acid has a very low pH, whereas retinol doesn’t like to be in a low pH,” says Fu.

Most anti-ageing creams don’t list the amount of each active ingredient they contain, which makes it hard to assess their likely efficacy. Mahto’s advice is to use a gentle cleanser and sunscreen in the morning (which will also function as a moisturiser), and then a make-up remover, cleanser and moisturiser in the evening. If you want to experiment with active ingredients, she suggests using a serum, as these tend to be more concentrated and penetrate the skin more effectively than creams, “but add only one new product at a time and pay attention to how your skin responds”.

You may not need to buy separate products for day versus night, either, provided your morning routine includes an SPF, says Emma Wedgeworth, a dermatologist and spokesperson for the British Skin Foundation, a medical charity. “I will always use separate sun protection and active ingredients, so I use the same moisturiser morning and evening, just with different supporting products,” she says.