Why Dry Skin in Winter?

Here are the reasons for dry skin in winter:

1. Indoor Heating
The amount of water vapour (moisture) in the air is called humidity. Cold air's ability to hold on to water vapour/moisture is low - and hence it is always dry. Warm air, on the other hand, tends to be more humid because its ability to hold on to water vapour/moisture is higher.
In winter, the air outside is cold and dry. The cold, dry air seeps indoors. This cold, dry air is heated up by indoor heating. Once heated up, its ability to hold onto moisture increases. But there is no moisture in the air outside. The heated warm air needs moisture. This warm air tries to grab onto any moisture/water vapour it can find. The water in our skin becomes the target - the warm air sucks the water in our skin. Skin loses its hydration and it becomes dehydrated.

2. Reduction in Sebum
Sebum is the oil that is secreted by the oil glands in our skin. The quantity of sebum in our skin determines the extent to which our skin is oily. Sebum helps the skin in its barrier function.
The visible layer of skin works like a barrier: It protects the skin from attacks from environmental irritants and prevents water loss from the skin.
If the amount of sebum reduces, the barrier function is compromised. In the winter months, the cold air strips our skin of its natural oils. Hence our skin has less sebum/oil.
Lower amounts of sebum compromise the skin's barrier function. Water loss from the skin increases and the barrier cannot prevent attacks from environmental irritants effectively. Loss of water leads to dehydrated skin. Attacks from environmental irritants lead to sensitive skin with lots of breakouts.

3. Slowing of Cellular Turnover
New cells are formed in the lower layer of skin regularly. These new cells, travel upwards through the various layers of skin and reach the visible layer of skin. Once they reach the visible layer, the old cells fall off and make way for the newer cells. This whole process is called cellular turnover. If the cellular turnover does not take place at the required pace, it means the old cells are stuck on the visible layer and are not being replaced by newer cells. This slow cellular turnover leads to a dull, flaky appearance.
In winter, cellular turnover slows down. This contributes to dull, dry skin.

4. Skincare Routine
In winter, the skincare routine has to change. It has to address the problems that winter brings to our skin. Products that can prevent water loss from the skin, facial oils, products that can strengthen skin's barrier function, regular exfoliation and a humidifier can help.
If we don't adjust the routine, skin gets drier and drier.

5. Legs and Hands
In winter, legs and hands get drier than our faces. This is because legs and hands have fewer oil glands than our faces. So they have less sebum/oil to help the skin in its barrier function. So legs and hands have less oil, to begin with (irrespective of the season). This is further exacerbated by a reduction in sebum in our skin in winter (see point 2).

6. Hot showers
In winter we tend to have hot showers. Hot water burns our skin- can be a mild burn but it still is a burn. Burns strip our skin of its natural oils, fats and lipids (all these 3 help our skin in its barrier function). Loss of these 3 means, that the skin's barrier function is compromised. This means water evaporates easily and skin becomes sensitive and irritated. This leads to dry skin.
Applying a moisturiser after a shower and keeping the water lukewarm can help.