Lisa Hipgrave, Director of IFRA UK, takes an in-depth look at creating stable and safe fragrances.
 

I have worked in the fragrance industry for 33 years and most of that time was working within fragrance creation. Now, as the Director of IFRA UK, I work with a range of companies across the UK promoting the safe creation, development and enjoyment of fragrances. By using an IFRA UK member, companies have the reassurance that they are dealing with professionals for whom quality, safety, compliance and excellence are considered essential.

Creating a new fragrance can be one of the most exciting and inspiring jobs around, however, it is not as easy to do as you might think. Through my training as a perfumer, in this article I woudl like to take you on the journey most perfumers would travel when creating a fragrance and the chemistry involved in making the magic happen.

The visceral nature of scent and olfaction is, of course, one of the joys of perfumery but this instinctual aspect of our reaction to fragrance means it can be hard to describe. This is why perfumers need a full description of what is required: the product, who will buy it and to what products it will ultimately be applied. This should include the odour profile sought, alongside which fragrances on the market appeal – and which do not.
 

For example, if the character of a fragrance is to be dominated by woody notes, you will include those as your starting point. I often compare this to creating a painting or artwork. If you know your work is to hang in a blue room, you know that pink colours bring out green tones more than blue would, so you adjust your palette of colours accordingly. It is similar with odours.

To help envisage this, take patchouli, which can be a big, solid odour that other materials can compliment or accentuate. Sandalwood, too, has a big base note effect, so you must take that into account with the top and middle notes you select. You might want to create a deliberate ‘clash’. In fact, the profile might refer to whether a smooth, well-rounded fragrance is required or whether contrasting, almost clashing, notes are preferred.  In the 1980s, the ‘overdose effect’ was particularly prevalent – this is when a fragrance is characterized by using specific ingredients in far higher concentrations than is normal and the fragrance is built around that distinctive note. Although this was very fashionable in the 80s it had to some degree been used in classic fragrances created decades earlier.
 

When creating a fragrance, a perfumer must think of the odour direction, strength and character, and also consider the base formula, price and any regulatory or other restrictions that may affect the chosen ingredients.  

If you are looking to create something with a fresh citrus note you need to consider which materials you can use to prolong the citrus fresh notes throughout the fragrance life, as many citrus ingredients are top note materials and quite fleeting in nature.

 

If a spicy fragrance is required it can pose stability and regulatory challenges, as many spicy materials have stability issues and some are IFRA restricted, including eugenol, cinnamic aldehyde and methyl eugenol which are found in many natural spice oils.
 

When creating a fragrance there are numerous things to consider – its suitability not just in terms of odour direction, target market and geographical destination, but also stability, compatibility, colour and regulatory compliance.
 

Ensuring total product suitability is very important. It means you are complying with any regulatory requirements around the selected ingredients, and from a business perspective it is important for product acceptability – consumers are less likely to purchase products that appear different or unstable, and regulations can affect the labelling of the product, which can also influence consumers.  
 

Fragrance molecules are full of functional groups with varying degrees of reactivity, so when raw materials are mixed together to create a fragrance compound, interactions are inevitable.
 

It is important to be aware of the maturation time of the fragrance you are creating. This is the time it takes for reaction rates to reach equilibrium in a fragrance compound. It is also important to have an understanding of what is happening on a molecular level. A number of different reactions can occur.
 

Interactions can take place internally between fragrance molecules. Concentration and storage conditions also affect this; however, these reactions are easier for perfumers to predict as they know exactly what was put into the fragrance compound and at what concentration.
 

Some of these reactions between fragrance molecules can lead to stability issues such as colour changes. Examples of this include ‘Shiff’s bases’ – Hydroxycitronellal when added to a fragrance compound along with Methyl Anthranilate form a Schiff’s base and the resulting reaction can affect both odour and physical appearance. In fact, these two materials can be purchased ‘ready reacted’ which helps to minimize the continued reactivity over time.
 

Reactions can also occur between the fragrance and base, these reactions are more difficult to predict so whenever possible, it is beneficial for customers to send in the base and its formula so the most suitable fragrances can be created. If you don’t minimize the reactions between the fragrance and base it can lead to a host of reformulation issues later.
 

Solvents are sometimes used to influence the overall polarity of fragrance compounds – polar solvents are used for hydrophilic bases and non-polar solvents for lipophilic bases. In order to improve solubility, non-ionic surfactants are sometimes added as a premix with the fragrance (in a specific ratio) before being added to the base.
 

Issues with clarity can occur in silicone bases, which are non-polar. This can be reduced by reducing the number of polar aroma chemicals in the fragrance or reducing the amount of silicones – or changing the packaging!

 

External influences such as light and temperature also affect fragrance stability. To ensure a fragrance is stable you need to ask: Is it compatible with the base and is it stable at the briefed dosage; in the final packaging; and in expected storage and usage conditions?
 

Fragrance development will take time, with many experiments taking place as additional ingredients are added and the formula is refined and altered.  During the creative process, the perfumer will be constantly smelling and using the fragrance in its intended base to ensure it is as close to the anticipated scent, or the ‘picture’, that was in their mind from the briefing stage.

Full stability tests are then carried out to predict the long-term stability of products in a range of environments, this may also lead to refinement and further modification.