Trend of Diffusers: Pleasant Fragrance with Risks

Aroma diffusers have quietly taken over our homes, workout spaces, and workplaces. They promise relaxing evenings and help mask unpleasant smells. The market for essential oils is booming. The U.S.‑based Cleveland Clinic notes that global sales are set to grow by billions of dollars in the coming years. But what is behind this trend? What advantages do diffusers really offer and what side effects should you know about? This report summarises current research and offers tips for safe use.

What are diffusers and how do they work?

Diffusers disperse essential oils as a fine mist into the room. There are several technologies:

• Ultrasonic diffusers: A piezoelectric element vibrates at high frequency to break up a mixture of water and oil into tiny droplets. These devices are quiet and double as humidifiers. However, they produce volatile organic compounds (VOCs) and particles. In a laboratory experiment with lemon, lavender, eucalyptus and grapeseed oils, diffusers emitted several milligrams of essential components within 15 minutes. The dominant particle sizes ranged between 10 and 100 nanometres; the smallest particles came from lemon oil and the largest from grapeseed oil. Simply switching from distilled to tap water increased particulate emissions fivefold when using eucalyptus oil.

• Nebulising diffusers: These devices atomise pure oil without water using a stream of air. They provide an intense scent but consume more oil and result in greater VOC exposure than ultrasonic models.

• Evaporative diffusers: A fan blows over a felt pad or reed sticks soaked with fragrance oil. These operate without heat but offer little control over the release rate of the scent.

• Heat diffusers: Oils are warmed on a ceramic plate or in a fragrance lamp. Heat speeds up evaporation but may also break down oils and create additional by‑products.

Benefits: what does aromatherapy promise?

Many people use diffusers to enhance their well‑being. There is some scientific evidence that certain essential oils, when used correctly, can have positive effects:

• Stress reduction and sleep: A review of 30 studies on aromatherapy and sleep quality found that lavender, citrus and rose scents reduced stress, pain and fatigue and improved sleep. Another review of 27 studies showed that aromatherapy significantly decreased anxiety in patients awaiting surgery. In clinics, lavender fragrance is used to lower blood pressure and heart rate.

• Mood enhancement: Aromatherapy massages with scents such as bergamot, rose or chamomile can ease depressive moods and improve overall mood. Scent molecules travel via the olfactory nerve directly to the limbic system, which controls emotions.

• Versatile uses: Oils like tea tree, peppermint or eucalyptus have antimicrobial properties. They are used for colds to ease breathing. However, such applications should be discussed with medical professionals because dosage is critical.

Despite these positive aspects, the Cleveland Clinic notes that aromatherapy is not a substitute for medical treatment and that the benefits depend on the correct selection and dosage of oils.

Risks and drawbacks – what diffusers release

Unregulated ingredients and VOC exposure

In many countries, essential oils are not strictly regulated. An independent analysis of 24 commercial oils identified 188 different VOCs, including 33 substances classified as hazardous. Toluene, a solvent, was detected in half of the products. These compounds evaporate into room air during diffusing. A chamber experiment showed that lemon oil diffused in an ultrasonic device released 2.6 mg of d‑limonene and lavender oil released 1 mg of linalyl acetate within 15 minutes.

When inhaled, VOCs rapidly enter the lungs and bloodstream. According to the U.S. Environmental Protection Agency, high VOC concentrations can cause eye, nose and throat irritation, headaches, coordination problems and damage to the liver, kidneys and central nervous system. Indoor VOC levels are typically 2 to 5 times higher than outdoors. In one test, VOC emissions from a single diffuser remained below Japanese limits for toluene , but the researchers caution that even low concentrations might be harmful and long‑term effects are unknown.

Fine particles and nanoparticles

Diffusers emit ultrafine particles along with fragrance molecules. The above‑mentioned study measured up to 3 mg/h of PM₁ particles from lemon and grapeseed oils, primarily sized between 10 and 100 nanometres. Emissions increased fivefold when eucalyptus oil was diffused with tap water instead of deionised water.

Researchers at Purdue University discovered that fragrances react with ozone, producing billions of nanoparticles. These particles are so small that they can penetrate deep into the lungs and potentially reach other organs. In a “Tiny House Lab”, the team found that scented wax melts and diffusers produce at least as many particles as candles and that these newly formed nanoparticles can occur at high concentrations in indoor air.

Allergies and toxic components

Many essential oils contain allergens. The German consumer platform Utopia cites the Federal Institute for Risk Assessment (BfR) and the Swiss Federal Office of Public Health: some compounds such as estragole, methyleugenol and safrole are considered potentially carcinogenic. Natural and synthetic fragrances alike can cause contact allergies and skin irritation.

Diffusers pose particular risks for infants and young children. The BfR warns that even tiny amounts of essential oils may trigger convulsions or respiratory arrest in babies. For children under three years, Utopia recommends using diffusers only with water (without oil) as humidifiers or avoiding them altogether.

Pets are also sensitive to fragrance compounds. Oils such as clove, tea tree, cinnamon or birch are toxic to cats and dogs because animals metabolise these substances differently.

Cognitive effects

A randomised study in a simulated office tested how diffuser emissions influence cognitive performance. Fifty‑nine participants inhaled lemon scent, deionised water or unscented grapeseed oil. The scented exposure shortened reaction time but significantly impaired impulse control and memory, leading to more impulsive decisions.

Tips for safe use of diffusers

To enjoy fragrance without harming your health, follow these guidelines:

1. Limit exposure: Less is more. Smart Air recommends running a diffuser for only 15 minutes to one hour and not using multiple oils every day.

2. Choose high‑quality oils: Use pure, organically grown oils free from synthetic additives and solvents.

3. Ventilate well: Open windows during and after diffusing to reduce VOC and particle levels.

4. Avoid use around children and sensitive groups: Babies, young children, pregnant women, chronically ill individuals and pets should not be exposed to fragrance oils.

5. Clean the device: Regular cleaning prevents mould and bacteria from growing in the water reservoir.

6. Combine with an air purifier: Activated carbon filters can absorb VOCs. If you run a diffuser, an air purifier with a carbon filter can reduce exposure, although it may weaken the scent.

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   Consider natural alternatives: Dried herbs, citrus peels or potted plants emit mild natural scents without chemicals. Often, regular ventilation is enough to eliminate unpleasant smells.