Fragrances enhance the appeal of cosmetic products, not only masking undesirable smells but also positively influencing mood and well-being [1]. Both natural and synthetic fragrances are used to create unique scents, with over 3,000 substances of which about 10% are of natural origin. Typically, monomolecular fragrances are not used alone; instead, combinations of various molecules (sometimes up to 300 per perfume) [2]. However, while fragrances can elevate a product’s sensory profile, their complex chemical compositions significantly increase the risk of skin sensitization.

Common allergens found in fragrances, such as limonene, linalool, and cinnamal—common in both natural and synthetic fragrances—can oxidise upon air exposure, forming compounds that trigger sensitisation and allergic reactions [5]. Symptoms of fragrance allergies include redness, itching, and rashes, which can occur even after low-level, repeated exposure. These issues are particularly concerning for leave-on products, where fragrances remain on the skin for extended periods.

Both natural and synthetic fragrances can carry allergenic risks, particularly in leave-on products. Industry guidelines recommend specific concentration thresholds to minimise allergic risk—0.01% for rinse-off products and 0.001% for leave-on products. Under EU cosmetics regulations, 26 fragrance ingredients must be listed individually if their concentration exceeds specific limits. If fragrances are used below threshold levels, they can be labeled more generally as “parfum” or “aroma” on ingredient lists. In June 2023, the European Commission added 56 new fragrance substances, including several oils and extracts, that must also be disclosed on product labels. In total, 80 fragrance ingredients now require listing to help consumers with allergies avoid potential allergens [6]. 

Essential oils are widely used in cosmetic formulations for their antimicrobial properties, anti-ageing benefits, and pleasant aromas. However, their use also presents challenges:

• Standardisation Difficulties
  Essential oils are complex mixtures of 20–60 compounds, with dominant ones comprising 20–70% of the blend [7]. Variations in plant genetics, growing conditions, and harvesting practices make them difficult to standardise, leading to inconsistencies in quality and efficacy.
• Oxidation Risks
  Like synthetic ingredients, essential oils can oxidize over time, forming compounds such as oxides and peroxides that are more allergenic. For example, oxidation products of (+)-limonene and α-pinene are significantly more sensitising than their original forms. Proper storage in cool, dark places and airtight containers is crucial to minimise this risk [7].
• Potential Toxicity
  Some essential oils, while beneficial in low concentrations, can exhibit toxic effects if used improperly. For instance, tea tree oil and lavender oil, widely regarded for their antimicrobial properties, have been associated with skin irritation and hormonal disruptions in certain cases.
• Recognized Allergens
  Many essential oils contain allergens such as linalool, eugenol, and geraniol, which are regulated and must be declared on cosmetic labels if their concentrations exceed 0.01% for rinse-off and 0.001% for leave-on products [6, 7].

Despite these challenges, essential oils remain a cornerstone of natural cosmetics. Advances in standardisation and quality control are gradually improving their reliability, ensuring they can be used safely in formulations.

Synthetic fragrances are valued for their stability, consistency, and affordability, making them essential for large-scale cosmetic production [8].

Key Benefits:

• Stability: Their chemical composition is predictable and easier to standardise, ensuring consistent product quality [9].
• Cost-Effectiveness: Producing synthetic fragrances is often cheaper than sourcing natural alternatives.
• Allergen Control: Synthetic fragrances can be tailored to exclude known allergens, reducing sensitisation risks [10].

Drawbacks:

• Toxicity Concerns: Some synthetic ingredients, such as phthalates, have raised health and environmental concerns [11].
• Oxidation: Certain synthetic molecules may oxidise and trigger allergic reactions if improperly stored [12].
• Consumer Perception: Many consumers view synthetic fragrances as less eco-friendly compared to natural alternatives.

Fragrance-free products are formulated without added scents and are recommended for individuals with sensitive skin or allergies. These formulations minimize the risk of irritation by focusing on functional, gentle ingredients. Research shows that fragrance-free options are generally safer for regular use, making them increasingly popular among consumers seeking mild, low-risk skincare.

Many brands are now embracing the demand for fragrance-free products as part of a broader movement toward more inclusive and environmentally friendly skincare solutions.

Fragrances in cosmetics enhance product appeal but pose significant challenges, particularly for sensitive skin. While natural fragrances like essential oils offer compelling benefits, they are not without risks, such as variability and allergenic potential. Synthetic fragrances, on the other hand, provide stability and cost-effectiveness but may raise concerns about health and environmental safety.

As consumer awareness of allergens and eco-friendliness grows, the demand for fragrance-free and hypoallergenic formulations continues to rise. By balancing innovation in fragrance technology with transparency and safety, the cosmetics industry can cater to diverse consumer needs, offering products that are both enjoyable and responsibly designed.

1. Pichon, A.M., et al., Sensitivity of Physiological Emotional Measures to Odors Depends on the Product and the Pleasantness Ranges Used. Frontiers in Psychology, 2015. 6: p. 1821.

2. Ahmed F., Mirza F. Fragrances and their effects on public health: A narrative literature review //Environmental Health Association of Quebec: Quebec, QC, Canada. – 2020.

3. Heisterberg, M.V., et al., Fragrance mix II in the baseline series contributes significantly to detection of fragrance allergy. Contact Dermatitis, 2010. 63(5): p. 270-276.

4. Martins, M.S.; Ferreira, M.S.; Almeida, I.F.; Sousa, E. Occurrence of Allergens in Cosmetics for Sensitive Skin. Cosmetics 2022, 9, 32. https://doi.org/10.3390/cosmetics9020032 

5. de Groot, Anton C. "Fragrances: contact allergy and other adverse effects." Dermatitis 31.1 (2020): 13-35.

6. Scientific Committee on Consumer Safety . Commission Regulation (EU) 2023/1545 of 26 amending Regulation (EC) No 1223/2009 as regards labelling of fragrance allergens in cosmetic products, 26 July 2023. Available from: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32023R1545 

7. Sharmeen, J.B.; Mahomoodally, F.M.; Zengin, G.; Maggi, F. Essential Oils as Natural Sources of Fragrance Compounds for Cosmetics and Cosmeceuticals. Molecules 2021, 26, 666. https://doi.org/10.3390/molecules26030666 

8. Sharmeen, J.B.; Mahomoodally, F.M.; Zengin, G.; Maggi, F. Essential Oils as Natural Sources of Fragrance Compounds for Cosmetics and Cosmeceuticals. Molecules 2021, 26, 666. https://doi.org/10.3390/molecules26030666 

9. Heisterberg, M.V., et al., Fragrance mix II in the baseline series contributes significantly to detection of fragrance allergy. Contact Dermatitis, 2010. 63(5): p. 270-276.

10. Havery, D.C. "Fragrance safety: Current concepts." Food and Chemical Toxicology, 1993. 31(3): p. 211-217.

11. Witorsch, R.J., and Thomas, J.A. "Personal care products and endocrine disruption: A critical review of the literature." Critical Reviews in Toxicology, 2010. 40(Suppl. 3): p. 1-30.

12. Hostynek, J.J. "Factors determining percutaneous metal absorption." Food and Chemical Toxicology, 2003. 41(3): p. 327-345.