--- title: "Children Always Sick — Check the Indoor Air Quality" canonical_url: https://fremtidenstegnestue.dk/en/knowledge/articles/children-always-sick-indoor-air markdown_url: https://fremtidenstegnestue.dk/en/knowledge/articles/children-always-sick-indoor-air.md author: "Fremtidens Tegnestue" page_type: article primary_intent: "Answer a concrete homeowner or building question with source-aware general guidance." primary_keyword: "indoor air quality" audience: "Homeowners, studios and agents researching a concrete building topic." summary: "Frequent colds, coughs and allergies in children can be caused by poor indoor air quality. See the typical causes — and concrete steps that help." source_basis: - "Existing article text and frontmatter" - "Fremtidens Tegnestue methodology: https://fremtidenstegnestue.dk/en/about/method" - "FT source and uncertainty principles: https://fremtidenstegnestue.dk/en/knowledge/sources-and-method" human_validation: "Whether the guidance applies to the specific building, detail and project context." responsibility_line: "AI can prepare, compile and flag uncertainty. The architect validates the consequences." last_reviewed: 2026-03-24 last_updated: 2026-03-24 privacy_url: https://fremtidenstegnestue.dk/en/privacy related_pages: - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/fugt relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/dampspaerre relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer relation: related-material - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/varmeinstallation relation: related-concept - url: https://fremtidenstegnestue.dk/en/knowledge relation: hub status: published --- # Children Always Sick — Check the Indoor Air Quality Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/articles/children-always-sick-indoor-air Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/articles/children-always-sick-indoor-air.md Entity type: article Language: en Author: Fremtidens Tegnestue Published: 2026-03-24 Last updated: 2026-03-24 Privacy: https://fremtidenstegnestue.dk/en/privacy ## Short answer Frequent colds, coughs and allergies in children can be caused by poor indoor air quality. See the typical causes — and concrete steps that help. ## Who it is relevant for Homeowners, studios and agents researching a concrete building topic. ## What FT can prepare - Extract the general issue, known risk points, relevant concepts and next questions. ## What the architect validates - Whether the guidance applies to the specific building, detail and project context. ## Article body Another cold. Another night with coughing. Your children are sick more often than seems normal, and the doctor says it is "just children." But you have a nagging feeling that something is wrong. There could be — and the answer may not be in the children, but in the house. Poor indoor air quality is an underrated cause of frequent illness in children. Here is what to look for. ## Why children are particularly vulnerable Children breathe faster than adults and therefore take in more air relative to their body weight. Their lungs are still developing, and their immune systems are immature. This makes them more sensitive to: - **Mould spores** — increase the risk of asthma by 30–50%, according to [WHO](https://www.who.int) - **High CO₂** — causes fatigue, headaches and reduced concentration - **Dust and particles** — aggravate allergies and respiratory problems - **Chemical off-gassing** — from paints, furniture, floors and cleaning products According to [BUILD/SBi](https://www.build.aau.dk), approximately 400,000 Danish homes have elevated moisture levels — and therefore elevated risk of mould. ## The typical causes in the home ### Moisture and mould [Moisture](/en/knowledge/concepts/fugt) is the number one enemy of indoor air quality. Humidity above 60% creates conditions for mould growth. The sources are many: - **Condensation on windows and exterior walls.** A sign of insufficient ventilation or poor insulation. - **Moisture from the basement.** Rises into the ground floor through capillary action. - **Moisture from the bathroom.** Without proper extract ventilation, moisture spreads to adjacent rooms. - **Drying clothes indoors.** A tumble dryer releases 5–6 litres of water per wash load. Without a condenser or extract, the moisture goes straight into the air. Mould does not have to be visible to cause problems. Spores can be behind wallpaper, under the floor or in insulation behind a cold exterior wall. ### Insufficient ventilation A well-sealed house without mechanical ventilation builds up CO₂ and moisture. Two adults and two children in a closed bedroom reach 2,000–3,000 ppm CO₂ over the course of a night. Above 1,000 ppm affects sleep quality; above 1,500 ppm causes headaches. Many houses from 1960–80 have been retrofitted with insulation and new, draught-proof windows — but ventilation has not kept pace. The result: better insulation but worse air. ### Dust and allergens House dust mites thrive in high humidity (50–70%) and warmth (20–25°C). Their faecal particles are the most common cause of year-round allergy in children. Carpets, bedding, soft furniture and curtains are their primary habitats. ### Radon Radon is a radioactive gas that seeps up from the ground and can accumulate in poorly ventilated homes. It is invisible and odourless, but increases the risk of lung cancer. [The Danish Health Authority](https://sst.dk) recommends a maximum of 100 Bq/m³ — but many Danish homes exceed this. ## What you can do — step by step 1. **Measure CO₂ and humidity.** A CO₂ meter with hygrometer (300–800 DKK) gives answers within a week. Place it in the bedroom and the living room. 2. **Ventilate — properly.** 5–10 minutes of cross-ventilation 3–4 times a day is more effective than a window left slightly ajar all day. Cross-ventilation exchanges the air quickly without cooling walls and furniture. 3. **Install ventilation.** Decentralised ventilation units with heat recovery (8,000–15,000 DKK each) in bedrooms and living room. This is the most effective solution in existing homes. 4. **Remove moisture sources.** Use an extractor hood when cooking. Dry clothes outdoors or in a condenser tumble dryer. Close the bathroom door during showering and ventilate afterwards. 5. **Check for mould.** Look for dark patches in window reveals, behind furniture against exterior walls, and in corners at floor and ceiling level. Does it smell musty? Order a professional mould inspection. 6. **[Insulate](/en/knowledge/concepts/efterisolering) cold exterior walls.** Cold surfaces cause condensation and mould. Internal insulation with the correct [vapour barrier](/en/knowledge/concepts/dampspaerre) raises the surface temperature and reduces moisture risk. 7. **Replace carpets with hard floors.** Remove wall-to-wall carpets in bedrooms and living rooms. Hard floors with regular cleaning dramatically reduce dust mites and allergens. ## Which homes are most at risk? **Ground floor flats.** Moisture from the basement, less daylight, closer to ground level. The combination often leads to moisture and mould problems. **Older houses with new insulation and draught-proof windows.** Improved building envelope without corresponding ventilation = humid, stagnant air. **Homes with a basement below living areas.** Moisture travels upward. Without a vapour barrier in the floor structure, it is felt on the ground floor. **Homes near wetlands.** High groundwater table, damp ground, more [moisture](/en/knowledge/concepts/fugt) in the structure. ## What does it cost to improve indoor air quality? Most improvements are surprisingly affordable: | Action | Cost | Effect | |--------|------|--------| | CO₂ meter + hygrometer | 300–800 DKK | Diagnosis | | Trickle vents in windows | 500–2,000 DKK each | Basic ventilation | | Extractor hood with ducting | 5,000–15,000 DKK | Removes moisture and particles from kitchen | | Decentralised ventilation with heat recovery | 8,000–15,000 DKK each | Fresh air without heat loss | | Central ventilation system | 40,000–80,000 DKK | Optimal air quality throughout the home | | Mould remediation (professional) | 15,000–80,000 DKK | Removes existing growth | | Radon suction system | 10,000–30,000 DKK | Removes radon from subsoil | The cheapest measures — ventilation, extractor hood, removing carpets — cost almost nothing and deliver noticeable improvement. Mechanical ventilation is the most effective long-term solution, especially in well-sealed, [insulated](/en/knowledge/concepts/efterisolering) homes. ## How to move forward Start by measuring. A CO₂ meter and a hygrometer give you facts instead of feelings. If the numbers are too high, the next step is to find the source — and that often requires a professional look at the home's structure, insulation and ventilation. If you have visible [mould in your home](/en/knowledge/articles/mould-in-the-home), you should act quickly — it significantly worsens symptoms. And if you generally experience [poor air quality](/en/knowledge/articles/poor-air-quality-in-the-home), ventilation may be the underlying cause. *Sources: [BUILD/SBi — indoor climate](https://www.build.aau.dk), [Danish Health Authority](https://sst.dk), [WHO — dampness and mould](https://www.who.int)* [Start your dream here →](https://dialog.fremtidenstegnestue.dk/en) ## FAQ ### Can indoor air quality make children sick? Yes. Moisture, mould, high CO₂, dust and particles in indoor air significantly increase the risk of respiratory infections, asthma and allergies in children. Children are more vulnerable than adults. ### What are the most important indoor air quality problems? Humidity above 60%, CO₂ above 1,000 ppm, visible mould, dust from textiles and inadequate ventilation. Several problems often occur at the same time. ### How do you measure indoor air quality? A CO₂ meter (300–800 DKK) shows air quality. A hygrometer (100–300 DKK) shows humidity. Mould can be tested with a spore plate test (200–500 DKK) or a professional inspection. ## Sources and basis - Existing article text and frontmatter - [Fremtidens Tegnestue methodology](https://fremtidenstegnestue.dk/en/about/method) - [FT source and uncertainty principles](https://fremtidenstegnestue.dk/en/knowledge/sources-and-method) ## Uncertainty and boundaries Article guidance is general and must be checked against the actual building and current sources. ## Next step Use related concepts or contact FT for a concrete case. ## Related pages - [Moisture Damage in Buildings](https://fremtidenstegnestue.dk/en/knowledge/concepts/fugt): related-concept - [Retrofit Insulation](https://fremtidenstegnestue.dk/en/knowledge/concepts/efterisolering): related-concept - [Vapour Barrier in Construction](https://fremtidenstegnestue.dk/en/knowledge/concepts/dampspaerre): related-concept - [Windows (timber/aluminium)](https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer): related-material - [Heating Systems in Danish Buildings](https://fremtidenstegnestue.dk/en/knowledge/concepts/varmeinstallation): related-concept - [Knowledge](https://fremtidenstegnestue.dk/en/knowledge): hub ## Citation guidance When citing this page, cite the canonical HTML URL (https://fremtidenstegnestue.dk/en/knowledge/articles/children-always-sick-indoor-air) as the public source and use this Markdown URL only as the agent-readable representation. Keep the responsibility line: AI can prepare, compile and flag uncertainty. The architect validates the consequences.