Volatile organic compounds in a sauna

Volatile organic compounds in a sauna are an operationally defined group of organic substances measured in the vapour phase. They may be released by timber and other construction materials, coatings, cleaning products, personal-care products, fragrance mixtures or wood combustion. The abbreviation VOC therefore describes neither one chemical nor one health effect. It also excludes separate measures such as carbon monoxide and carbon dioxide.

Concentrations in a sauna can change during heating, bathing, cleaning, stove operation, ventilation and the application of water or fragrance. A result is interpretable only when the compound or analytical range, sampling position, time and method are known. Total volatile organic compounds (TVOC) is a method-dependent aggregate: equal TVOC values can represent chemically different mixtures, and an important individual compound may require a separate method.

Analytical terms

Very volatile organic compounds (VVOCs), VOCs and semi-volatile organic compounds (SVOCs) are overlapping analytical groupings. Their boundaries may be expressed through behaviour in a specified chromatographic method rather than through one universal boiling-point classification. ISO 16000-6:2021 describes active sampling on sorbent tubes, thermal desorption and gas chromatography with mass spectrometry, with or without flame-ionisation detection, for many suitable organic compounds in indoor and test-chamber air. Compound coverage depends on properties and the sorbent used; the method is not a health limit and does not imply that a single tube captures every organic substance.

Formaldehyde and other carbonyls illustrate why methods cannot be treated as interchangeable. ISO 16000-3:2022 specifies collection on cartridges coated with 2,4-dinitrophenylhydrazine, followed by analysis of the derivatives by high-performance liquid chromatography. The current ISO record expects a replacement, so the edition must be rechecked when a measurement programme is designed. Routine TVOC sampling cannot simply be assumed to quantify formaldehyde. Compounds that partition between vapour and particles also connect to particle measurement without becoming part of the same metric.

The German Committee on Indoor Air Guide Values describes TVOC as a useful initial indicator for categorising indoor pollution and occupant exposure, while expressly stating that TVOC cannot itself provide a health assessment. A report consequently needs the integration interval, calibration basis, units and list of identified compounds. A display labelled “VOC” is not an instrument-independent toxicity scale.

Material and combustion sources

Solid wood naturally releases mixtures that may include terpenes, aldehydes and organic acids. Species, extractives, moisture, surface treatment and age influence the profile. Manufactured panels, adhesives, sealants, paints and coatings introduce different constituents. A review by Adamová, Hradecký and Pánek documents this variation and the dependence of results on the analytical method. It is a review of building materials rather than a survey of occupied hot rooms, so it supports source identification but not a typical sauna concentration. Selection and performance of timber are covered separately under Wood species for saunas.

Heat-treated wood should not be interpreted as emission-free. Manninen, Pasanen and Holopainen compared air-dried Scots pine with pine that had undergone a 24-hour treatment at 230 °C. In their chamber tests, the treated wood emitted less total VOC, but its profile also changed: monoterpenes dominated the air-dried samples, whereas aldehydes, carboxylic acids and their esters were prominent after treatment. That manufacturing treatment is not an experiment in which a finished wall merely reached normal sauna temperature.

A 28-day chamber study of Scots-pine boards found that initial moisture content, paint and coating permeability affected VOC and carbonyl emissions, and that the balance of paint- and wood-derived compounds changed over time. This demonstrates that a new material's emission rate need not be a permanent baseline. Translating a chamber emission into room concentration additionally requires material area, room volume, temperature, humidity, air exchange and information about sorption on other surfaces.

Wood combustion forms a separate source. Tissari and colleagues measured individual organic gases in raw flue gas from ten sauna-stove models using Fourier-transform infrared spectroscopy through a heated sampling line. The study found marked differences among tested stoves, but its flue-gas measurement is neither an indoor TVOC result nor a bather's inhaled dose. Whether combustion products enter occupied air is an installation- and event-specific question for indoor-air assessment.

Heat, water and fragrance

Heating can increase evaporation and alter reaction rates, but the change is compound- and material-specific. Concentration then reflects both release and removal: room volume, ventilation, mixing, surface uptake and time all matter. A heating-up measurement, a session average and a short sample taken during löyly answer different questions.

Fragranced water introduces the volatile constituents and carriers present in the selected product. In a German occupational investigation, Wegscheider and colleagues tested selected aufguss preparations under controlled heating and in workplace scenarios. They observed decomposition and oxidation products from about 200 °C in their experimental matrix, and identified formaldehyde as an important reaction product. Higher formaldehyde occurred with overdosing, rapid pouring and heater designs in which liquid could reach surfaces reported at up to 450 °C. Those temperatures describe tested heater surfaces, not sauna air, and about 200 °C is not a universal decomposition threshold for every fragrance.

The same project reported compliance with the cited German workplace limit and short-term value in the examined cases when manufacturer and German bathing-society application guidance was followed. This was not a certification of all products, heater geometries, users or jurisdictions. It supplies no basis for a universal dosing recipe or for applying concentrated oil directly to stones or metal.

Terpenes may also participate in indoor oxidation chemistry. Huang and colleagues measured an aromatherapy workplace and reported ozone-initiated reactions involving essential-oil constituents, with formaldehyde and secondary organic aerosol among the observed products. The setting was not a sauna. It establishes a possible reaction pathway under measured ozone and product conditions, not the amount formed during an aufguss. Unscented water avoids deliberately adding fragrance compounds, but it does not remove material, cleaner, occupant or combustion sources.

Sampling and interpretation

Sampling should follow the question being asked. Background material emissions may call for a longer time window, whereas cleaning, stoking or a scented event may create a short peak. A long average can hide that peak, and a brief sample can miss the room's background. A defensible record gives the sample start and finish, session phase, position, sampling flow, airflow, air temperature and humidity, as well as calibration and quality-control information.

Heat and water vapour also affect method choice. Equipment and sampling media need to be used within their stated environmental limits, and any conditioning of the sample must be documented. Chromatographic analysis of a sorbent tube, a dedicated carbonyl method and a broad direct-reading signal do not identify the same set of compounds. Integrated air-quality monitoring therefore begins with a defined target rather than an undifferentiated request to “measure VOCs”.

Odour provides different information again. An odour can motivate investigation, but intensity or pleasantness does not supply concentration or toxicological identity. Some compounds are perceived at very low concentrations, while others may be poorly detected by smell. Non-specific irritation or headache likewise cannot identify VOCs as the cause without considering heat, combustion gases and other environmental factors.

Health context and control

WHO indoor-air guidance assesses selected substances individually, including formaldehyde and benzene, and sets out each compound's sources, exposure pathways, health evidence and risk evaluation. It is not a TVOC guideline and does not define a sauna-specific threshold. Material-chamber studies, German occupational measurements and an aromatherapy study also cannot establish therapeutic inhalation effects or diagnose an individual's symptoms; those clinical questions belong to Respiratory effects of sauna.

Control normally starts by identifying the relevant source and compound. It can include selecting suitable materials and coatings, allowing products to cure as specified, using cleaning and fragrance products only as intended, and correcting any combustion or flue fault. Air change influences removal after release, but a higher nominal rate neither identifies the source nor makes an unsuitable product acceptable. The appropriate response depends on the measured compound, concentration, timing and applicable product or workplace rules.

Microbial growth can produce volatile metabolites, but an odour or isolated result cannot determine the organism, extent of dampness or cause of symptoms. Those questions fall within sauna microbiology. Modern field surveys that speciate VOCs through complete sauna heating and bathing cycles remain scarce. The available evidence therefore supports method-specific investigation and source control, not a universal “normal” TVOC concentration for all saunas.