Winter Itch and Winter Dry Skin

Dryness of the Skin: Xerosis (pronounced Zerosis)


James Channing Shaw, MD

If you look with a magnifying lens at very dry skin, it looks like a dry lakebed, with multiple shallow cracks. The medical name for this dryness is xerosis. How does xerosis happen, who gets it, and what can be done to treat it?

Normally the skin acts as a barrier to evaporation; water is prevented from escaping by the top most layer of the skin called the stratum corneum. In this layer skin cells are stacked on top of each other, each one overlapping the ones below. Each stratum corneum cell contains material called keratin that is nearly impermeable to water. Between the cells is a mixture of lipids (fats), called the lipid layer.



This multlayered sandwich of cells and lipids creates an armor that protects against water loss. However, since we are all different, some individuals have better functioning stratum corneum than others and are better protected from drying out. Those of us who are genetically unlucky in this regard are susceptible to dry skin, primarily from two environmental causes. One is decreased humidity in the air and the other is a damaged lipid layer. Low humidity pulls water from the cells of the stratum corneum, making them brittle, curled at the edges, and separated. Add wind to the dry air and the problem gets worse.


Damaged lipid layer comes from chemicals on the skin that wash away the lipids. Our hands are the most susceptible to this kind of damage because they have the least amount of lipid in the stratum corneum layer. Ironically it is our hands that get most exposed to chemicals such as soap and detergents. Solvents like alcohol, cleansers, and ammonia are even worse. With the amount of hand washing we have all been taught to do, it is no surprise that dry cracked hands are a common problem in the winter.

Severe xerosis: this case has become erythema craquelé

 
Why is winter air such a problem? Two reasons: 1) cold air holds less moisture than warm air, and 2) artificial heat in our homes dries the air to extremes. Indoor humidity of less than 10% is common during a cold winter. Only the heartiest of stratum corneum can withstand this desert-like effect without becoming dry and cracked.

When skin dries out, most people start itching. The shins and the lower back are the most common places for ‘winter itch’. Faces and lips can also become dry, flaky and cracked. The hands are different: finger tips can split and are very painful. While this can be annoying and uncomfortable, the good news is that very little serious illness comes from skin dryness.

So….what to do? There are basically two ways to minimize the problem: 1) increase humidity in the air, and 2) provide skin barrier protection against water loss. A vacation in the tropics returns skin to normal within a week or two. The increased humidity in the warm air of the tropics stops water loss from skin. A humidifier, while not as good as a tropical environment, can be helpful in your home. For dry cracked hands, a lesson from feet is instructive. Feet don’t dry out as commonly as hands because they are protected all day in warm humid shoes and socks. Gloves provide the same protection for hands that sox do to for feet. Soft comfortable gloves, not rubber gloves, are best. The goal is to increase humidity, not cause perspiration and soaking.

For more skin barrier protection, additional ‘lipid layer’ needs to be applied. There is an important lesson here concerning lotions, creams, and ointments. Lotions are mostly water with some oil (lipid) and when applied to the skin, the water evaporates leaving a small amount of oil remaining. This gives the false impression of 'absorption', but lotions help only in the mildest cases of dryness. Severe dryness calls for thick creams (less water, more lipid), or ointments like petroleum jelly (all lipid, no water). The greasy ointments give the best protection but take some getting used to.

The worst cases of dryness may require professional help and prescription treatments. For splits in the hands, cover with tape or a bandage which helps the pain and speeds healing. Soaking hands in warm water for 10 minutes puts some moisture back if a thick cream or ointment is applied immediately, followed by gloves. The same is true for the whole body: a plain water soak for 10 minutes followed immediately by greasy creams or ointments can help the driest skin. The secret is to not let the water evaporate before applying moisturizers. Apply the cream or ointment within 60 seconds. It takes a while to get used to the greasy feel but the improved moisture in the skin should be apparent within a few days.

Finally, two common misconceptions deserve mentioning:
1. Applying moisturizers does not shut down your skin’s ability to make its own oil. It is safe to use moisturizers as much as needed; the skin will not become dependent on them.
2. Moisturizers per se will not prevent aging of the skin unless they contain sunscreens.