The arithmetic nobody does
Consider a week in February for someone who surfs three times and works indoors.
Time in cold water and cold wind: perhaps six hours across the week, some of it with the face covered by a hood. Time in heated indoor air: something like a hundred hours, all of it with the face, hands and often the forearms fully exposed.
Even if the outdoor exposure were more intense per hour, which it sometimes is and sometimes is not, the indoor exposure is an order of magnitude longer. People attribute their winter skin to the sessions because the sessions are memorable. The hundred hours are not memorable, which is precisely why they are not managed.
What heating actually does
The mechanism is covered in the article on cold air and is worth restating in one line: warming air raises how much water it could hold without adding any, so its relative humidity falls, and the drier the source air, the further it falls.
British winter outdoor air is cold and therefore low in absolute water content. Heated to a comfortable indoor temperature, its relative humidity can fall a long way. That is the air your face is in from the moment you get to work until the moment you go to bed, and then all night.
The things that make it worse than it needs to be
Forced air heating and vehicle heaters. These do not merely warm the air, they move it. Moving air strips the boundary layer, which raises loss further at the surfaces it blows across. Anyone who drives to and from sessions with the heater on full at the windscreen is applying a wind exposure to a face that has just come out of the sea.
Sitting close to a heat source. Radiant heat raises skin temperature, which raises the vapour pressure at the surface, which raises the gradient. A shin close to a wood burner is having a much worse evening than a shin two metres away.
Hot showers at both ends of the day. Hot water mobilises intercellular lipid and warm skin loses water faster while it is warm. A long hot shower on cold, salt covered skin followed by a heated room is a very efficient way to strip and then desiccate a barrier.
Hand washing indoors. Every wash is a pH and lipid event, and indoor life supplies many of them.
The bedroom, which is a third of it
Eight of those hundred hours a week become fifty six if you count the nights, and they are the most controllable of the lot because nobody else is in the room negotiating the thermostat.
A cooler bedroom is better for skin for the same reason it is generally recommended for sleep. If a room must be heated, keeping it modestly heated and out of the direct path of the airflow makes a real difference. And the overnight period is the one window in which a heavy application will stay where you put it, which is discussed in the article on the repair window.
| Exposure | Mechanism | How much control you have |
|---|---|---|
| Room temperature | Sets the gradient across the whole indoor day | High at home, often none at work |
| Airflow at the face | Strips the boundary layer, like wind | High, it is usually a vent direction |
| Shower temperature and length | Mobilises intercellular lipid, then desiccates warm skin | Complete |
| Hand washing frequency | Raises pH and removes lipid repeatedly | Partial, and none where hygiene requires it |
| Bedroom conditions | Longest single uninterrupted exposure | Usually complete |
| Absolute humidity of the air | The underlying driver | Partial, and adding water has consequences |
Ordering framework written by this publication from general skin physiology. It is not a measurement, it is not taken from any study, and no number in it is a reading.
Adding water to the air
The direct fix for a low absolute humidity indoors is to add water to the air. It works, because it reduces the gradient, and that is not in dispute.
What we will say alongside it is what most publications leave out. British housing stock has a widespread condensation and damp problem, and adding water vapour to a poorly ventilated room in winter can make that worse. Water added to indoor air condenses on the coldest surfaces, which are usually external walls, window reveals and the corners behind furniture. A humidifier also needs cleaning, and a neglected one is a poor thing to sleep next to.
So the sequence we would suggest is: heat less first, because it is free and has no downside; ventilate properly, because it prevents damp; and only then consider adding water, with attention to where it will condense. We are not naming equipment and we are not going to.
The laundry point
Drying clothes indoors adds a significant quantity of water to indoor air. That is genuinely useful for the gradient and genuinely risky for condensation, and which of those dominates depends on your ventilation.
For people in wet sport there is a specific version of this: wetsuits, towels and boots drying inside a small flat put a lot of water into the air of that flat. If your windows stream and your corners are black, that is your ventilation telling you something, and the answer is ventilation rather than stopping the drying.
The dull conclusion
You cannot control the weather and you can control the thermostat. For a British winter the indoor levers are heat less, keep moving air off your face, shorten and cool the showers, wash fewer things, and put something on before the long stretches rather than after them.
None of that is interesting and all of it is more effective than another purchase.