Plain water is as much a beauty product as the expensive skin tonic you buy for your face, say experts.

Adequate water intake enables our skin to stay smooth, supple and flexible, said Dr Rachael Teo, an associate consultant dermatologist at Changi General Hospital.

When we are dehydrated, our skin loses its natural firmness and flexibility.

Dr Alvin Wong, medical director of SKN MediAesthetics, explained that this is because water facilitates the supply of vital nutrients and oxygen to skin cells.

If there is an inadequate supply of water, harmful toxins will build up, he said. The skin's health will suffer and skin problems might occur or get worse.

We need to drink about two to three litres of water daily although the actual amount for each of us depends on factors such as body weight and activity level, said Dr Teo.

However, there is no need to get carried away.

Although water does go a long way in maintaining good skin health, drinking large amounts does not guarantee a flawless complexion.

Dr Wong said many other factors combine to determine how dry or oily the skin is. External factors like the environment and skin care regimen, biological factors like genetics and the number of oil-producing glands and their functions all come into play.

Many people also believe that drinking lots of water can get rid of dry skin. Unfortunately, this is not true, said Dr Teo. To combat dry skin, one should apply moisturiser regularly, she said.

Another point to note: excessive contact with water, such as frequent washing of the face or hands, may actually dehydrate the skin further.

When water evaporates, this causes increased transepidermal water loss from the skin, she said. Transepidermal water loss is when moisture from the skin's deeper layers is drawn to the surface and gets lost via evaporation.

In addition, tap water has the tendency to strip away oils that seal in moisture, said Dr Wong.

A common result of excessive dryness is hand dermatitis, where the skin becomes itchy and inflamed.

The increasing popularity of foods and beverages with cosmetic claims is also a cause for concern.

Dr Teo said we should find out what goes into such products before buying them as they may contain undesirable ingredients such as high sodium or sugar content.

'With the numerous advertisements in the media, it is often difficult to discern what is truly effective," she said.

'It is best to stick to a well-balanced diet to meet the daily requirement for vitamins and minerals that our body and skin needs."

This article was first published in The Straits Times.