Hair Care Fragrance: Siloxane Evaporation Impact

Leave-On Hair Care Fragrance Substantivity: The Siloxane Evaporation Effect

In hair care formulation, ingredients that evaporate quickly can fundamentally alter the final scent profile a consumer experiences. A 2013 study led by researchers Montemayor, Price, and van Egmond, published in the Journal of Cosmetic Science, provides concrete data on how cyclopentasiloxane (D5), a common volatile carrier, behaves on hair and skin, with direct implications for fragrance performance.

D5 Evaporates Rapidly, Carrying Initial Fragrance with It

Montemayor, Price, and van Egmond’s research centered on a practical question: after applying a personal care product, how much of the volatile ingredient D5 actually gets washed into wastewater? To find out, they applied commercial hair care products containing D5 to human hair tresses. They then collected and analyzed the rinse water at specific intervals: immediately after application, and then 8 and 24 hours later. The team used isotope dilution headspace gas chromatography/mass spectrometry (GC/MS) for precise measurement.

The results were clear. “Significant amounts of D5 in ‘leave-on’ application products evaporate during typical use,” the authors state. For hair care, the concentration of D5 available to go down the drain was only a tiny fraction of what was first applied. This happens because D5’s molecular structure—a cyclic arrangement of silicon and oxygen atoms with methyl groups—gives it very low surface tension and high vapor pressure. These properties make it an excellent, fast-drying solvent and carrier in formulations, but also cause it to vanish from hair and skin within hours.

This rapid evaporation is a double-edged sword for fragrance. When a hair serum is first applied, D5 acts as a solvent, helping to evenly distribute fragrance oils across the hair fiber. However, as the D5 evaporates, it actively transports a portion of the fragrance’s more volatile top notes into the air. This creates the initial, often intense, burst of scent but can also deplete the overall fragrance reservoir on the hair, potentially shortening its lifespan. The study’s methodology did not specifically track individual fragrance molecules, but the fate of the carrier solvent strongly implies a significant change in the scent composition left behind.

Formulating for the Scent That Remains, Not Just the Scent Applied

For perfumers and product developers, this research reframes a key challenge. The fragrance brief for a leave-on hair product cannot be based solely on the scent in the bottle or immediately upon application. It must account for the scent profile after the primary volatile carrier has departed. The olfactory character will shift as the more volatile fragrance components, aided by D5’s evaporation, are lost.

This necessitates a strategic approach to the fragrance formula. To achieve longer-lasting fragrance substantivity on hair, the ratio of middle and base notes may need to be increased relative to top notes. Ingredients with higher molecular weight and lower volatility, which have a stronger tendency to adhere to the hair’s protein structure, become more important. The interaction between fragrance oils and other non-volatile components in the formula—like polymers, oils, or cationic conditioners—becomes the primary determinant of lasting scent. Understanding emulsion stabilization and ingredient interactions is therefore directly relevant to this outcome.

A limitation of the study is its focus on a single, specific siloxane (D5). Other volatile carriers, like alcohol or lighter-weight linear siloxanes, will have their own evaporation rates and interactions with fragrance. However, the principle established is broadly applicable: in systems designed for quick drying, the carrier’s evaporation is a dominant force shaping fragrance delivery and longevity.

Practical Implications for Hair Care Development

This evaporation dynamic has several concrete effects on formulation and testing. First, it alters the risk assessment for ingredients. Because so little D5 is rinsed off, its direct aquatic loading from leave-on hair care is lower than a simple formula percentage would suggest. However, the study did not investigate indirect environmental pathways, such as evaporation to the atmosphere.

Second, it changes how product performance should be evaluated. In-house testing should move beyond assessing the initial “bloom” of fragrance. Controlled studies using hair tresses, similar to the research methodology, can track how the scent profile evolves over 8 to 24 hours of wear. This provides data to fine-tune the fragrance oil blend. Techniques like fragrance encapsulation could be adapted for hair care to create a timed release, counteracting the initial loss from carrier evaporation.

Finally, it highlights a key difference between product categories. While D5 evaporates quickly from leave-on hair and skin care, its journey in a rinse-off conditioner or shampoo is completely different, as it is immediately washed down the drain. Similarly, the goal for a long-lasting hair fragrance differs from that for a laundry detergent, where substantivity to fabric is the primary mechanism.

Conclusion

The study by Montemayor and colleagues provides measurable evidence that volatile carriers like cyclopentasiloxane do not remain on hair. Their rapid evaporation actively shapes the fragrance experience by removing volatile components, shifting the scent’s character over time. Effective formulation requires anticipating this shift and building a fragrance oil designed to perform after the carrier has gone.

Sources:
https://pubmed.ncbi.nlm.nih.gov/23186890/