A routine that works through the summer often produces dryness or irritation in winter without anything being changed. The cause is a set of measurable environmental differences acting on the skin barrier.
Cold air carries less water
The amount of water air can hold falls sharply as temperature drops, so outdoor winter air is dry in absolute terms even at high relative humidity.
Water moves from skin toward drier air, and the drier the surroundings, the faster that loss occurs.
Heating that air indoors lowers its relative humidity further, which is why indoor winter environments are frequently drier than the outdoor conditions people are avoiding.
Barrier lipids change consistency with temperature
The lipid matrix holding the outer skin layer together is more ordered and less flexible at low temperatures.
A stiffer matrix cracks more readily under the mechanical stress of movement and friction from clothing.
Those microscopic cracks increase water loss and allow irritants access, which is the physical basis of winter roughness and stinging. Rapid temperature swings between cold outdoors and heated interiors add repeated stress to the same structure.
Skin adjusts its own production seasonally
Sebum production falls at lower temperatures, reducing the surface film that slows evaporation.
The composition of the barrier lipids themselves shifts between seasons, and the natural moisturising factors within skin cells vary in concentration.
These adjustments take weeks, which is why the difficult period tends to be the transition rather than the depth of a settled season.
Summer brings a different set of problems
Heat and humidity increase sweating and sebum production, and occlusive products that suited winter can trap both and contribute to blocked follicles.
Ultraviolet exposure rises substantially, and its effects on pigmentation and on ageing changes accumulate rather than resolving with the season.
Air conditioning reintroduces a dry indoor environment in summer, which is why some people find their skin dries in both extremes.
Adjusting formulation rather than adding steps
Winter usually calls for richer emollients that slow evaporation, while summer favours lighter textures that do not occlude.
Reducing the frequency of exfoliating and strongly active products during cold months lowers the total load on a barrier already under stress, which is often more effective than adding a further product to compensate.
Skin that cracks, bleeds, weeps or fails to improve with these adjustments may have an underlying condition such as eczema, and that is a reason to see a doctor rather than to keep changing products.