Dry skin happens when your skin’s outer barrier loses moisture faster than it can replace it. This barrier is remarkably thin, just 10 to 20 cells thick, but it relies on a precise mix of fats and water-trapping molecules to keep skin hydrated. When something disrupts that balance, whether it’s the weather, a hot shower, or your own genetics, the result is the tightness, flaking, and roughness you recognize as dry skin.
How Your Skin Stays Hydrated
Understanding what goes wrong starts with understanding what’s supposed to happen. Your outermost layer of skin, the stratum corneum, works like a brick wall. Dead skin cells are the bricks, and a mortar of specialized fats holds them together. This fat layer is about half ceramides, with the rest split roughly equally between cholesterol and free fatty acids. That 2:1:1 ratio is critical. When it shifts, water escapes through the gaps.
Inside those skin cells sits a blend of water-attracting molecules collectively called natural moisturizing factor, or NMF. It’s made up of amino acids, lactic acid, urea, and various mineral salts. These molecules pull water from the environment and hold it inside the cell, keeping skin plump and flexible. NMF is produced when a structural protein called filaggrin breaks down inside the skin cell. If your body makes less filaggrin, you produce less NMF, and your skin dries out from the inside.
Genetics and the Filaggrin Connection
Some people are simply built to have drier skin. The most well-studied genetic factor is a mutation in the FLG gene, which provides the blueprint for filaggrin. Filaggrin does double duty: it bundles structural proteins together to physically strengthen the skin barrier, and its breakdown products become the NMF molecules that keep skin hydrated. It also helps maintain the slightly acidic pH that healthy skin needs to function properly.
About 8 to 10 percent of the general population carries an FLG gene mutation. Among people with eczema (atopic dermatitis), that number jumps to 20 to 30 percent. If you’ve dealt with persistently dry, easily irritated skin since childhood, genetics may be playing a significant role, and no amount of moisturizer will fully override a filaggrin deficiency, though it can help manage symptoms.
Hot Water and Long Showers
Hot water is one of the most common and least recognized causes of dry skin. Higher water temperatures disorganize the fat structure in your skin barrier, making it more permeable. Essentially, the heat loosens the “mortar” between skin cells. On top of that, prolonged water exposure causes the skin cells themselves to swell and creates pools of water in the spaces between cells, which disrupts the lipid layers that are supposed to sit there in an organized, tightly packed arrangement.
The damage continues after you step out of the shower. Hot water exposure increases the rate at which moisture evaporates from the skin surface. Studies measuring water loss through the skin consistently find higher evaporation rates after hot water contact compared to cold. This is why your skin can feel tight and dry within minutes of toweling off, especially during winter when indoor humidity is already low.
Soaps, Cleansers, and Surfactants
The foaming agents in soaps, body washes, and household cleaners damage the skin barrier through two distinct mechanisms. First, surfactant molecules can wedge themselves into the fat layers between skin cells, disrupting the organized packing and making the barrier more fluid and leaky. Second, and often worse, surfactants can physically extract fats from the skin, stripping away the barrier material entirely.
Which of these two things happens depends on the type and concentration of surfactant. Harsh cleansers, particularly those containing sodium lauryl sulfate, tend to both insert into and extract from the lipid layer. This is why your hands can feel raw after washing dishes without gloves, or why switching to a gentler cleanser sometimes resolves dry skin that no moisturizer could fix. The problem isn’t that your skin lacks moisture. It’s that the barrier keeping moisture in has been chemically stripped away.
Aging and Dry Skin
Dry skin becomes dramatically more common with age. A meta-analysis pooling data from 28 studies found that 53 percent of older adults have clinically dry skin, with the highest rates in nursing homes and in developed countries. The prevalence was similar in men and women, and the lower legs were the most commonly affected area.
Several things change as you age. Your skin produces fewer of the natural fats and NMF components that maintain hydration. Sebaceous glands shrink and produce less oil. Cell turnover slows, meaning the barrier doesn’t repair itself as quickly after damage. These changes are gradual, which is why dry skin tends to creep up in your 50s and 60s rather than arriving overnight. Regular use of leave-on moisturizers containing humectants (ingredients that attract and hold water) has been shown to meaningfully improve skin hydration in older adults.
Low Humidity and Cold Weather
Dry air pulls moisture from your skin the same way it dries out a wet towel. In winter, you get hit twice: cold outdoor air holds very little moisture, and heated indoor air is even drier. The steeper the difference between the water content in your skin and the water content in the surrounding air, the faster moisture evaporates from the skin surface. This is why people who never think about dry skin during summer can develop flaking and cracking every December.
Air conditioning creates a similar effect in warm climates. Desert and high-altitude environments are particularly harsh because the ambient humidity stays low year-round. If your dry skin follows a seasonal or geographic pattern, the environment is almost certainly a primary driver.
Thyroid Disease and Skin Hydration
Hypothyroidism, where the thyroid gland doesn’t produce enough hormone, is one of the most common medical conditions that causes dry skin. The mechanisms are surprisingly varied. Thyroid hormone normally regulates how skin cells grow and mature. When levels drop, cells can overproduce a tough structural protein called keratin, leading to thick, scaly patches. Low thyroid hormone also reduces the activity of an enzyme needed to produce cholesterol sulfate, which in turn triggers filaggrin production. Less filaggrin means a weaker barrier and less NMF.
Hypothyroidism also disrupts the formation of tiny structures in skin cells that help build the waterproof barrier, and it decreases sweat gland output, removing another source of surface moisture. If your dry skin appeared alongside other symptoms like fatigue, weight gain, or sensitivity to cold, a thyroid check is worthwhile. Treating the underlying condition often improves the skin.
Nutritional Deficiencies
Your skin can’t build a functional barrier without the right raw materials. Linoleic acid, an omega-6 fatty acid, is the most abundant polyunsaturated fat in the skin and a critical component of the barrier. It gets incorporated into a specific type of ceramide that is essential for preventing water loss through the skin surface. Your body cannot manufacture linoleic acid on its own, so it must come from food. Sources include sunflower seeds, walnuts, soybean oil, and many nuts.
True essential fatty acid deficiency is uncommon in people eating a varied diet, but it can occur with very restrictive diets, certain malabsorption conditions, or prolonged low-fat eating patterns. When it does, dry, scaly skin is one of the earliest signs.
Medications That Dry Your Skin
Several categories of medication can cause or worsen dry skin as a side effect. Retinoids (used for acne and anti-aging) speed up skin cell turnover faster than the barrier can keep up. Diuretics reduce fluid levels throughout the body, including the skin. Cholesterol-lowering statins can interfere with the skin’s own cholesterol production, which matters because cholesterol is one of the three essential barrier fats. If your dry skin started or worsened around the time you began a new medication, the timing may not be coincidental.
Overwashing and Friction
Frequency matters as much as water temperature. Washing your hands 20 times a day, even with mild soap, doesn’t give your skin barrier enough time to rebuild between exposures. Healthcare workers, food service employees, and parents of young children are particularly susceptible. Physical friction from rough clothing, excessive exfoliation, or even vigorous towel-drying can mechanically remove the top layer of skin cells before they’ve finished forming a complete barrier. Patting dry instead of rubbing, and limiting exfoliation to once or twice a week, gives the barrier time to do its job.