Dry skin, referred to medically as “xerosis,” is a very common condition. Characterized by scaly or flaky skin, it results from either excess water loss at the surface or inadequate replenishment from within. It can occur anywhere on the body, but more commonly affects areas that are exposed, such as hands and face, and areas with poorer circulation, including legs. It is influenced by both genetic and non-genetic factors, each playing more or less of a role in different individuals.
Genetics & Age
Genetically, there is at least one factor linked to dry skin (the “filaggrin” gene) that is quite common throughout the world. There are thousands of variations in this gene, such that some affected individuals do not notice dry skin until later in life while others suffer from dry skin and itchy rashes as early as infancy.
Among non-genetic factors, age is a consistent determinant of dry skin. Skin invariably gets drier with age, in large part due to thinning of the outer layer of skin. Women often note a dramatic change in their skin around menopause, suggesting that hormones also play a role. Age-related dry skin usually starts out mild, localized (e.g., affecting hands or legs), and/or limited to the colder seasons. Over time, if not managed, it will tend to worsen and be more chronic.
Cold weather is the most obvious external factor contributing to dry skin. Cold air holds less moisture than warm air. Additionally, when that cold air comes into your home and is heated up, the air is expanded, which makes the relative amount of moisture even lower. In other words, your skin is drying out not only when you are outside, but also, and typically more so, when you are inside.
Many surface exposures can cause or contribute to dry skin. Detergents act by binding to and removing oily substances, including the surface lipids that help prevent water loss. Thus, harsh soaps are quite drying. Long hot showers are notorious for drying the skin as higher temperatures soften the protective lipids allowing them to more easily be stripped from the skin. The alcohol in many hand sanitizers and disinfectants disrupt bonds between water molecules, allowing water to evaporate more readily from our skin surface.
Medications that decrease water or fat in the body can also contribute to dry skin. Systemic retinoids, such as the acne-fighting medication Accutane, decrease oil production allowing excess water loss and as a result dry skin. Topical retinoids (including prescription tretinoin and over-the-counter retinols) have similar effects to systemic retinoids. (Retinoids also increase turnover of the skin, contributing to the appearance of flakiness.) Cholesterol-lowering “statins” (e.g., simvastatin, lovastatin) likewise lower the amount of necessary protective lipids in the skin. Diuretics used for blood pressure control (e.g., hydrochlorothiazide, furosemide) decrease circulating blood volume and hence diminish the delivery of water, lipids, and important protective components to the skin.
Some medical conditions also predispose to dry skin. Hypothyroidism is commonly associated with dry skin (as well as dry hair, brittle nails, and other skin changes). Dry skin can also be seen in diabetes and heart disease. All of these conditions are associated with reduced blood circulation, and since blood is what carries water and essential protective factors to the skin, dry skin is a common consequence. Certain vitamin deficiencies, and malnutrition in general, can cause skin to become drier due to lack of lipids or structural components in the outer layers of our skin that help keep moisture locked in.
Dry skin becomes problematic when it leads to irritable or itchy skin. Those with a strong genetic basis to their dry skin have an increased risk of “atopic dermatitis” (or “atopic eczema”) – a skin condition that often, although not always, presents by childhood and is characterized by extremely itchy skin. However, anyone with dry skin can develop itchy rashes. Rashes that result “purely” from dry skin (in actuality, there is probably always some irritating factor at play) are described by several terms, such as “asteototic eczema,” “dry skin eczema,” “eczema craquelae,” or “nummular eczema.” This would include the localized or limited itchy rashes that appear in the wintertime or the more generally itchy skin seen commonly in the elderly. Itchy rashes that follow exposure to a known irritant are termed “irritant dermatitis,” “irritant contact dermatitis,” or “irritant eczema.” This would include hand eczema due to frequent hand washing, itchy outbreaks following use of a new facial exfoliative cream, or the annoying itch caused by a wool sweater. Irritant eczema can occur without underlying dry skin, but having dry skin makes it more likely and more severe.
So how do we manage dry skin? There are a number of preventative measures that dermatologists recommend. Use mild soaps to minimize stripping of lipids from the skin. Likewise, wear gloves when washing dishes or handling household cleansers. Daily showers are okay, but keep them cool or lukewarm. If dry skin is a problem in the wintertime, purchase a humidistat to monitor indoor humidity and place humidifiers throughout the house or at least in rooms where the majority of your time is spent. During the wintertime, try to maintain a humidity above 35% and as close to 40% as possible (40-50% is ideal during warmer months).
Treatment consists of moisturizing. Moisturizers range in consistency: lotions are more liquid, creams are thicker, and ointments are similar to Vaseline. If not indicated on the label, a good rule-of-thumb is that lotions often come in pumps while creams and ointments require squeeze tubes or sealable jars. The heavier the consistency, the better its moisturizing property. Those with severe dryness and/or eczema require creams and ointments. Ointments also tend to contain fewer additives including alcohols and are therefore the best choice if irritation or allergy is a concern. The best time to moisturize is immediately after a shower or bath, essentially to lock in moisture before it has had the chance to evaporate from the skin. At least once a day is ideal, but more is better for moderate to severe dryness and/or eczema. Finally, ceramide-containing moisturizers are likely to yield additional benefits for those with moderate to severe dry skin. Ceramides are an important lipid in our skin that protects against water loss. These moisturizers not only seal in moisture, they help restore and maintain the barrier preventing excessive water loss.
As a final note, scaly skin does not always equate to dry skin. Certain rashes can mimic dry skin, especially when mild. Common among these are seborrheic dermatitis (also known as dandruff) and periorificial dermatitis. Skin peeling that is a normal consequence of inflammation (known medically as “desquamation”), such as that occurring after a mild sunburn, can also be mistakenly interpreted as dry skin. Finally, precancerous sun damage (known medically as “actinic damage” or “actinic keratoses”) can sometimes present as broadly rough or flaky skin.
In summary, while the definition and diagnosis of dry skin are straightforward, the range of causes and presentations is quite broad. As such, the treatment guidelines will be different for everyone. If you are unable to manage your dry skin on your own, especially if it has led to distressing itch or does not seem like typical dry skin, please consult with your dermatologist.
Jane Yoo, MD