Guide

Dry air symptoms

What are the symptoms of dry air?

Dry skin and chapped lips, irritated eyes and airways, nosebleeds, more frequent static shocks, and timber or instruments shrinking and cracking. They cluster in cold weather because outdoor air at low temperatures carries very little water, and warming it indoors does not add any.

The symptoms

They arrive together, which is the clue that one cause is behind them:

Skin and lips. Dry, tight, cracking. Hands and lips first, because they are most exposed.
Eyes. Gritty and irritated, worse for contact lens wearers.
Nose and throat. Dryness, crusting, nosebleeds, a sore throat on waking.
Static. Shocks from doorknobs and car doors, clinging clothes, hair that will not behave.
Timber and instruments. Furniture joints loosening, floorboards gapping, guitars developing sharp fret ends.
Dust. More airborne, because it is not being weighed down by moisture.

Why they are seasonal

Here is the part most explanations get slightly wrong. The heating is not drying your air. Heating removes no water whatsoever.

What happens is arithmetic. Cold outdoor air carries very little water in absolute terms, however high its percentage reads. Bring that air inside — through doors, vents, gaps, ordinary ventilation — and warm it. No water is added, but the amount the air could hold rises steeply. The percentage collapses.

The same outdoor air, brought inside and warmed to 21°C. Nothing is added or removed.
Outdoor conditions	Water carried	Indoors at 21°C reads
0°C at 80%	3.9 g/m³	21%
−5°C at 85%	2.9 g/m³	16%
−10°C at 90%	2.1 g/m³	12%
10°C at 70%	6.6 g/m³	36%

A cold snap at −10°C produces indoor air drier than most deserts, and the outdoor forecast that day will say 90% humidity. That contradiction is the whole reason the absolute figure is worth watching — it is the one that predicts a dry indoor spell.

What actually helps

Adding water to the air. A humidifier is the direct answer, and it is the only thing on this list that addresses the cause. Keep it clean — a dirty reservoir aerosolises what is growing in it.

Not over-ventilating in very cold weather. Ventilation is exchanging your indoor air for extremely dry outdoor air. Enough for air quality; not more.

Drying laundry indoors. Normally advice to avoid, since it raises the dew point. In a very dry cold spell that is exactly what you want.

Protecting the surfaces that suffer. Moisturiser, lip balm, eye drops, and cases for instruments. Treating the symptom is reasonable when the cause is the outdoor climate.

What does not help: a bowl of water on a radiator, and houseplants. Both evaporate at a rate that is negligible against a room's air exchange.

How dry is too dry

Below about 30% most people notice it. Comfort guidance puts the healthy range at 30–50%, and there is no benefit to going below 40% — you would be trading dry-air problems for nothing, since mould and dust mites are already suppressed well above that.

The effects are gradual rather than threshold-like. 35% is fine for most people; 15% is uncomfortable for nearly everyone.

Not medical advice

This describes a mechanism, and the mechanism is real. But dry skin, nosebleeds, sore throats and irritated eyes all have plenty of other causes, and persistent or severe symptoms are worth taking to a doctor rather than blaming on the weather.

What this site shows

Outdoor conditions, including the grams of water per cubic metre that predict how dry your indoor air will be once that air comes inside and warms up. That is a genuinely useful early warning.

It also estimates the likely range for each of your rooms from those outdoor figures and how the room is used, or reads a HomeKit sensor if you have one. The estimate is a typical figure for that kind of room rather than a measurement of yours — no phone has a humidity sensor of its own.

Common questions

What humidity is too dry?

Below about 30% relative humidity most people notice dry skin, lips and airways. The effects worsen gradually rather than at a threshold, and 30–50% is the range comfort guidance recommends for occupied spaces.

Does heating dry out the air?

Not literally — heating removes no water at all. It raises the amount of water the air could hold, so the same water reads as a much lower percentage. The air was always that dry in absolute terms; warming it revealed the fact.

Why do I get nosebleeds in winter?

Dry air draws moisture from the mucous membranes lining the nose, which can crack and bleed as they dry. It is the most common seasonal explanation, though persistent or heavy nosebleeds are worth discussing with a doctor rather than attributing to the weather.

Does dry air make you more likely to get ill?

There is reasonable evidence that dry indoor air impairs the mucous clearance that traps pathogens, and that some viruses survive longer in it. It is one factor among many in why respiratory infections are seasonal, not the whole explanation.

Will a bowl of water on the radiator help?

Very little. Evaporation from an open bowl is slow relative to the air exchange of a whole room. It is not harmful, but it will not shift a room's humidity measurably.

Sources

ASHRAE Standard 55 — Thermal Environmental Conditions for Human Occupancy — Source of the 30–50% comfort range
WHO Guidelines for Indoor Air Quality — Dampness and Mould

Published 12 August 2026