Image copyright Getty Images Image caption Moisturiser holds the water in the skin and protects against dryness

Actress Helen Mirren has been quoted - in colourful language - saying that moisturiser probably does nothing at all for the skin. Is she right?

Not really. If you have dry skin, moisturiser does help by supplying water to the skin and trapping it there.

Most moisturisers contain a greasy substance that holds the water in.

Many years ago, moisturisers were very greasy on the skin - but now there are huge numbers of moisturisers and creams for sale, each one with a slightly different mix of ingredients.

The key, according to Dr Sweta Rai, from the British Association of Dermatologists, is finding one that suits your skin type and feels comfortable.

"A moisturiser's job is to maintain an outer armour on the skin, which prevents against infection and helps skin conditioning," she says.

"If you're using a good moisturiser for you, then it will be doing a good job for your skin."

Oil v water

For oily skins, she recommends lotions that contain more water.

For dry skins, the advice is to choose ointments or creams that contain a little more oil.

Dr Rai says "many people are probably using the wrong moisturiser".

Image copyright REUTERS/Eric Gaillard Image caption The Oscar-winning actress Helen Mirren is the face of one of L'Oreal's moisturiser ranges

Dr Rai suggests using a sun cream with a sun protection factor (SPF) of 30 as a moisturiser - that way it can protect against the Sun's rays, be reapplied regularly and keep the skin hydrated.

And she says it is possible to get a good moisturiser for under £10.

But standard moisturisers don't stop wrinkles or ageing, she says.

However, scientists who tested a cream with anti-ageing ingredients in 2012 did find that it appeared to smooth out wrinkles in some people.

As babies, we all start out with wonderfully smooth skin.

During puberty, glands in the skin start producing oil, and as we age, exposure to sun, cold weather and central heating systems all dry out the skin.

In winter the skin naturally dries out more, and in summer the skin naturally produces oils - but dry skin affects most people to some degree all year round.

It isn't a medical issue normally, but it can become one if the skin becomes sore, tender, itchy and inflamed.

An article from Harvard Medical School sets out the ingredients in moisturiser and explains why they help with dry skin.

water soaks into the skin

occlusives hold water in

humectants draw water up from the skin

emollients make the skin feel smooth

lactic acid makes skin more flexible

The article says: "You really can't go very wrong.

"Almost all the moisturisers on the market will help with dry skin, and in most cases, the choice comes down to subjective experience."

Tips for preventing dry skin