In the multi-billion pound beauty industry, hundreds of products claim to be all-powerful youth elixirs, but according to Dr Des Fernandes, vitamin A remains "the only effective anti-ageing cosmetic ingredient we have".

[Discover 9 ways you’re making your skin look older]

And he should know. The plastic surgeon has been studying the substance for more than 35 years, and believes "everyone in the world needs to use it".

And you can do that in the form of retinol skincare.

Retinol, put simply, is the base form of vitamin A, a substance that is metabolised into retinoic acid within the skin, and has "tremendous benefits" in terms of skin ageing.

"Studies on the effects of retinoic acid on the skin show that you'll see a dramatic change from wrinkled skin to smoother skin, and pigmented skin becomes much less pigmented," Dr Ferandes explains. "It makes more collagen and more elastin [which give skin its firmness], and results in thicker skin."

So why aren't we all slathering on this miracle-worker on the daily? Sadly, there is one drawback to retinol - but it's easily overcome, if you know how.

Here, Dr Fernandes explains the key points for reaping retinol rewards...

Firstly, give it time to work

"The problem with retinol is that it's an irritant. Most people will react to it, think they're allergic and throw it away, that's why we need to introduce it very carefully," Dr Fernandes says. "It varies from person to person, depending on their metabolism."

Start with a low dose 

"Start with very low doses and slowly let the skin adapt, before using more concentrated doses until eventually you're using the ideal amount," advises Dr Fernandes, to avoid redness and flaky patches.

Some products come with a barrier cream that you mix the retinol into a little at a time, or you can mix it with your usual moisturiser to temper the strength. Others come in varying concentrations, from mild to strong. It could take weeks or even months for your skin to acclimatise, but the results will be worth it.

Take note of the use by date

Retinol is a notoriously unstable substance, with a shelf life of around six months, so pay attention to the date indicator on the box, otherwise you'll continue to use an ineffective product.

[Read more: Why is my skin so dry? 10 reasons your face is dehydrated]

Use only at night

Retinol should be applied every night after cleansing. Avoid the delicate skin around the eye area, allow it a few minutes to absorb, then follow with your usual night cream.

But don't forget your SPF

"Retinol is photosensitising [meaning skin becomes more sensitive to the sun]," Dr Fernandes says, "so it's always a good idea to use an SPF." You want at least factor 15, applied every morning.