The Invisible Wall on Your Skin

The story

Run a finger along the back of your hand. That smooth surface is one of the cleverest walls ever built. The very top of your skin is made of tiny flat cells, stacked and overlapped like little bricks, and in between the bricks a soft, oily mortar holds the wall snug and sealed.

The wall has two jobs, and it does them every second of your life. It keeps the outside world out. And it keeps your water in. That second job is the one people forget. Your body is mostly water, and the air around you is always, quietly, trying to steal it. Water rises out through your skin all day long, and the oily mortar slows that escape to a gentle trickle your body can easily replace.

When the wall is working, you never notice it. But some things wear the mortar thin. Long hot showers and lots of soap can rinse away some of those precious oils, because soap cannot tell the difference between the grime it should take and the mortar it should leave. And then there is cold weather. Cold air is thirsty air. When air turns cold, it simply cannot hold much water. Then heaters indoors warm that same dry air and make it thirstier still. In a cold country in winter, the air sips at your skin all day, stealing water faster than the wall can hold it back.

You can feel what happens next. The skin may feel tight, or flaky, or itchy. Lips are often hit hardest, because lips barely have any of the skin's natural oil at all. Knuckles and cheeks often turn dry and sore too. Doctors in cold countries even have a name for it, winter itch.

This is where moisturiser comes in, and it is cleverer than it looks. A good cream is a little repair crew with three workers, and it brings a sip of water of its own. One worker lies over the wall like a thin raincoat, slowing the water's escape. Another, with a name like glycerine, is a water-grabber, pulling moisture up into the wall and holding it there. And a third settles softly in between the bricks, refilling the mortar itself. Moisturiser is not mainly about pouring water in. Its deeper trick is helping your wall gather water and keep it.

In a warm, damp place like Singapore, the outside air is already full of water, so the weather itself dries skin far less, though air-conditioned rooms have thirsty air of their own, and every person's skin is different. But visit a cold country in winter, and you may well feel your own skin start asking for help. That is why, in those lands, many people reach for cream after washing, as naturally as they reach for a coat. And for some children whose skin wall is extra leaky, with a condition called eczema, moisturiser is real medicine that doctors prescribe.

So if your skin ever feels tight after a bath, listen to it. A little cream, gently rubbed in, is you handing fresh mortar to a hard-working wall.