Q If I drink enough water, why do I still need to use moisturiser? How do I tell the difference between dry and dehydrated skin?

A Leona Low, training manager of Clarins, explains that the water we drink is used to regulate body temperature and to transport nutrients to our internal organs. What is left then goes towards hydrating the skin.

Skin dehydration occurs when the water and oil that form part of the protective layer of your skin are out of balance, she adds.

'This can happen for a number of external reasons, such as being in an air-conditioned environment, which have nothing to do with the amount of water we drink. So it is more effective to apply a hydrating skincare product directly to the skin for immediate absorption.'

As for the difference between dry skin and dehydrated skin, both conditions result in a feeling of tightness and roughness.

'But dry skin is caused by not having enough oil in the skin, and dehydrated skin is due to not having enough water in the skin,' she says.

One way to tell the two apart is to check for superficial fine lines on the forehead and cheeks, a common sign of dehydrated skin.

Press your palm against your cheek. If you see several thin, fine horizontal lines appear as you apply pressure and then disappear when you release the pressure, these are lines of dehydration.

It is common to have dehydration lines at any age, especially if you are exposed to air-conditioning for long periods, she explains.

For very dehydrated skin (for example, after coming back from a vacation in a dry, wintry climate), try Clarins' HydraQuench Cream-Mask ($65).

For more regular use, look out for lightweight moisturisers like Clarins' HydraQuench Smoothing Gel ($88), a gel that helps to control oil while hydrating your skin.

Signs of dry skin, on the other hand, include dull skin tone and fine lines that can eventually become deeper wrinkles and crow's feet.

Look out for richer products for dry skin, such as Shiseido's Benefiance Revitalizing Cream ($75), which is formulated for night-time use and helps to restore resilience to rough, dry skin.

This article was first published in Urban, The Straits Times.