6. What are the gaps in the current knowledge about perfume allergies?
Although the science has progressed, there are still gaps in clinical and epidemiological research. Amongst others, the SCCS opinion lists the following gaps:
- Clinical data on more fragrance substances are needed to assess more fully the epidemiology of fragrance contact allergy and pin-point the culprit substances for induction and elicitation of contact allergy in man. Data from a broader range of EU countries is needed, as difference in exposure and use habits are expected across Europe.
- Very little is known about susceptible groups of the population. Data are needed to qualify and quantify the increase in risk of susceptible groups in order to provide a better protection of all consumers.
- Aberrant enzyme activity in certain individuals, often related to genetic enzyme polymorphisms, may result in an increased or reduced risk of sensitisation to prohaptens in certain individuals or populations. More research into the role of relevant traits is needed.
- Dose-response data from clinical studies are available for only a few allergens. To establish individual safe levels, such data are required for all established allergens of concern and covering an appropriate range of product types.
- Data on human exposure to fragrances from the use of different product categories is very scarce and therefore does not provide an optimal basis of risk assessment. Exposure data on use for perfume/eau de cologne are for example lacking.
- Most experimental studies are done on individual fragrance ingredients, while exposure to allergens in cosmetic products is usually to mixtures of allergens. The risk of sensitisation and elicitation may depend on the mixture of substances, but very few studies on this exist.
- Screening in dermatitis patients should be performed with air-exposed samples of such fragrance substances that in experimental studies have been demonstrated to act as prehaptens.
- Patch testing should, if possible, be performed with the isolated true haptens formed from prehaptens and prohaptens to increase the possibility to diagnose allergy from these type of substances.
- There is a need for more experimental research to further establish the impact of the behaviour of fragrance substances when applied on the skin (including factors such as volatility, autoxidation, skin penetration, reactivity in skin and bio-activation).
Also, with regard to the animal data used in the opinion, several studies were of insufficient quality. Often, data on experimental results are not published but available only in company files and therefore not easily accessible.
Finally, applying only mechanism-based SAR as a tool in non-animal based risk assessment for skin sensitisation is of limited value for fragrance substances. This is due to major information gaps in the present model when addressing substances that act via activation, and the high incidence of such substances in fragrances.
Further experimental investigations of the sensitisation potential of fragrance substances are needed to determine the impact of the volatility of the substance as well as the effect of the vehicle on skin penetration/absorption and reactivity.
From a clinical perspective, it is important for the individual who is sensitised to one fragrance substance to know if they must also avoid other fragrance substances that can cause allergic contact dermatitis due to cross-reactivity. This is a field that has not been studied very much so far and needs to be focused on much more in the future. More...