What Happens to Indoor Air When You Use Perfume or Sprays?

What happens to the compounds that spread through a room after you use perfume or body spray? Once released into the air, these compounds do not necessarily just become more dilute. They can react with other substances to form new compounds or tiny particles.

In 2024, Tianren Wu and colleagues used five fragranced personal care products in a laboratory to investigate their emissions and how those emissions changed in air containing ozone. This was not a study testing whether symptoms occurred; it examined the contents of air that people might inhale. It points to the need to consider compounds formed after use, as well as those originally present in a product.

Examining Product Emissions Separately from Subsequent Reactions

The experiment used a perfume, a body spray, a dry-shampoo hair spray, a hand lotion, and a roll-on antiperspirant/deodorant. One commercially available product of each type was tested in a 62-cubic-meter chamber designed to resemble an office.

The researchers first measured volatile organic compounds, or VOCs, released directly from the products. They then added ozone to the room and measured the gaseous compounds and particles produced after the VOCs reacted. Ozone is a highly reactive gas; in this experiment, its concentration was maintained at 35–40 ppb.

The ventilation rates also differed between the two experiments. In the direct-emission experiments, the volume of air exchanged per hour was equivalent to three times the room’s volume; in the oxidation experiments, it was 0.65 times the room’s volume. Differences in concentrations between the two therefore cannot be read as the effect of adding ozone alone. The researchers also compared how compounds changed over time to distinguish direct emissions from reaction products.

More Than 200 VOCs, but Not All Behave Alike

Across the five products, more than 200 directly emitted VOCs were detected. With spray-type products, concentrations tended to rise sharply immediately after use and then decline. In contrast, the hand lotion and roll-on product continued to emit VOCs at relatively stable rates throughout the one-hour observation period.

The figure “more than 200” does not mean that this many harmful substances were found. VOC is a collective term for organic compounds that readily enter the air. Much of what the perfume and sprays released was ethanol, used as a solvent. When considering reactions with ozone, however, fragrance-related terpenes and their derivatives were important. The quantity emitted and the likelihood of reacting need to be considered separately.

Measuring instruments also have limits on the substances they can detect. The researchers note that they did not capture every emitted compound and that some compound names remain tentative assignments. Even when a molecular formula is known, the chemical structure cannot necessarily be determined uniquely.

Reactions with Ozone Produced New Gaseous Compounds and Particles

Under conditions with added ozone, a variety of oxidation products were detected. These are different substances formed when compounds released by the products react. The authors consider them to have arisen primarily through reactions between ozone and terpenes or their derivatives.

New particle formation was also observed after use of the hand lotion, hair spray, perfume, and body spray. Instruments that measure particle size tracked the appearance of extremely small particles and their growth over time. What the researchers followed was the formation and growth of new particles accompanying reactions of emitted gaseous compounds. The authors interpret low-volatility oxidation products, which readily move from the gas phase into particles, as contributing to this change. However, they did not establish every compound’s contribution or its magnitude.

During these four new-particle-formation events, the number concentration of ultrafine particles smaller than 100 nanometers reached peaks of approximately 34,000–200,000 particles per cubic centimeter. This is a measure of the number of particles, distinct from the particle mass concentration discussed below.

Under the same conditions, no new particle formation was observed with the roll-on product. Products differ in the compounds and quantities they emit. This exception matters: the findings cannot be extended to conclude that every fragranced product generates the same quantity of particles.

The Same Product Can Give Different Results under Different Room Conditions

In a supplementary experiment, ozone was lowered to 25–30 ppb while ventilation was increased to an hourly air exchange equivalent to 1.83 times the room’s volume. When the perfume, hair spray, and body spray were used under these conditions, the mass concentration of particles smaller than 1 micrometer was more than 50% lower than in the initial oxidation experiment, despite greater product use.

However, because both ozone and ventilation were changed, this cannot be described as “ventilation alone halved the concentration.” The amount of reactant available, how long compounds remain indoors, and particles already present also influence how many particles form next. The results indicate that the conditions of the space where a product is used need to be considered alongside the product’s properties.

Application methods also differed from everyday use. The sprays were released directly into the room air, not onto the body or hair. The lotion and roll-on product were spread on paper on a glass plate and left in the room for just one hour. They were not applied to skin warmed to body temperature. It is important to recognize that the experiment did not directly reproduce which compounds people inhale, or how much, during actual use.

What Is Known, and What Remains, When Considering Health?

An important feature of this study is that it followed both product emissions and compounds formed in the air after use. An ingredient list alone cannot fully describe the composition of the air people encounter after reactions have occurred. This also raises the question of whether studying only the original ingredients is sufficient when investigating health implications.

What the study measured, however, were concentrations and sizes of gaseous compounds and particles, not health outcomes such as headaches, asthma attacks, or mucosal irritation. This experiment alone also cannot establish the toxicity of the products formed or how the measurements correspond to people’s exposure in everyday environments. The formation of many particles does not prove the cause of a particular symptom, and comparing particle counts with those from other air-pollution sources does not mean their harmfulness is the same.

Recognizing this scope does not dismiss reports of feeling unwell around fragrances. Research on chemical reactions in air and research on human symptoms and disease examine different parts of the issue. The contribution of this study is to make more specific which compounds and conditions need further investigation to connect the two.

Summary

Compounds released from perfumes, sprays, and similar products changed into other gaseous compounds and new particles under the ozone-containing conditions set in this experiment. The changes differed by product and indoor conditions, and no new particle formation was observed with the roll-on product among the five products tested.

When considering the relationship between fragranced products and indoor air, it is useful to ask not only “What is in the formula?” but also “After use, what does it become, and under what conditions?” The extent to which those chemical changes translate into exposure and health effects in everyday life remains a question for further investigation.

References

Authors: Tianren Wu, Tatjana Müller, Nijing Wang, Joseph Byron, Sarka Langer, Jonathan Williams, Dusan Licina
Article title: Indoor Emission, Oxidation, and New Particle Formation of Personal Care Product Related Volatile Organic Compounds
Journal: Environmental Science & Technology Letters 11(10), 1053–1061 (2024)
DOI: 10.1021/acs.estlett.4c00353
Original full text: Open PDF in the Cyprus Institute institutional repository
Rights notice: © 2024 The Authors. Published by American Chemical Society. CC BY 4.0.