Radiator season: why your skin changes in October

Every year, somewhere in the second half of October, the appointments change. Eczema that was quiet all summer is back, hands are cracking, and a reliable number of people are convinced they have suddenly become allergic to a product they have used for years.

Almost none of it is an allergy. It is the heating.

What the season actually does

Cold outdoor air holds very little moisture. Heat that air to living-room temperature without adding any water to it and the relative humidity indoors falls off a cliff — a steam-heated New York apartment in January is, in humidity terms, closer to a desert than to the street outside.

Skin loses water to that air continuously. A healthy barrier slows the loss; a barrier that is even slightly compromised cannot keep up, and the result is the tight, itchy, flaking skin that shows up in the same four months every year.

So the problem is not the cold on your face for the ten minutes you are outside. It is the sixteen hours a day indoors.

The shower is the other half

Hot water feels wonderful on itchy skin and is one of the main reasons the itch returns worse an hour later. Heat and surfactants strip the lipids that hold the barrier together, and a long hot shower in a dry apartment is close to the worst possible combination.

What helps, in rough order of how much difference it makes:

• Shorter and cooler. Five to ten minutes, warm rather than hot. This is the single biggest change available and the least popular.
• Moisturise within about three minutes of getting out, onto skin still damp. Applied to damp skin, a moisturiser traps the water that is already there; applied twenty minutes later to dry skin, it is working with much less to hold.
• Thicker than you think. Ointments hold water best, creams are a reasonable compromise, and lotions are mostly water and alcohol and evaporate off. If it pumps easily and sinks in instantly, it is probably not doing much in February.
• Fragrance-free, including "unscented" products that contain a masking fragrance. Fragrance is the commonest contact allergen in skincare and winter skin is more permeable than summer skin.
• A humidifier in the bedroom. Eight hours a night of air that is not actively pulling water out of you is worth more than most products.

Hands are a separate problem with the same cause. Washing, sanitiser and cold air in combination produce a dermatitis that no amount of hand cream applied once a day will outpace — the cream has to go on after every wash, which in practice means one at the sink and one in a coat pocket.

When it is not just dry skin

This is the part worth the appointment, because several conditions arrive dressed as winter dryness and do not improve with any of the above.

Suspect something else when it is asymmetrical — one hand, one patch, one side. Ordinary dry skin is broadly even; a single stubborn plaque is usually a diagnosis.

Suspect something else when there are well-defined, thick, scaly plaques, particularly on elbows, knees or the scalp, and especially alongside nail pitting or joint stiffness. That combination is psoriasis, and it is a different treatment entirely.

Suspect something else when there is a ring with a raised, scaly border and a clearer centre, which is fungal, and which steroid cream will make temporarily better and ultimately worse.

And come in regardless if it is keeping you awake. Sleep-disrupting itch is not something to manage with a better moisturiser through to March; it is both treatable and, in its own right, a reason to be seen.

The short version

The air indoors is the cause, the shower is the accelerant, and the fix is cooler water, a thicker moisturiser applied to damp skin, and a humidifier at night. If one patch refuses to behave while everything else improves, that patch is the appointment.