Allergic contact dermatitis caused by farnesol: clinical relevance

CONTEXT

The fragrance material farnesol is cited as an infrequent but important cause of allergic contact dermatitis (ACD). It is included in the fragrance mix II patch series and requires labeling in the European Union if it is used in a consumer product.

OBJECTIVE

To review the existing literature to determine the causative role of farnesol in clinical contact allergy.

MATERIALS AND METHODS

Survey of the literature on farnesol studies; predictive and clinical elicitation tests in case reports, reviews, and abstracts.

RESULTS

Predictive animal studies demonstrated in most cases that farnesol was a nonsensitizer. However, 2 local lymph node assays (LLNAs) indicated strong sensitization potential. Predictive human test data indicated a low potential, if any, for sensitization in human tests with farnesol at 10% or 12%. A few clinical reports indicated low-level allergy or questionable reactions to farnesol, with 5% being the most commonly used. There were also reports in which no reactions were seen.

DISCUSSION

Predictive testing on farnesol in animals shows conflicting results depending on the study methodology used. Human predictive patch-test data also had gaps that prevented it from being definitive in pointing to a causative relationship between farnesol and contact dermatitis. The real sensitizing potential of a material can best be determined by evaluating the clinical and epidemiological data so as to help resolve the conflicting animal and human predictive test data.

CONCLUSIONS

This literature and scoring exercise showed that predictive and clinical elicitation data do not document a clear causative determination that farnesol is a frequent contact allergen. Detailed clinical relevance and patient studies should clarify the clinical problem farnesol represents.

Aqueous 2% geraniol as a mosquito repellent failed against Aedes aegypti on ponies

Organic insect repellents are of interest to many agricultural producers and animal owners. Geraniol, a plant-derived alcohol, is naturally produced by a wide range of plants and is a US Environmental Protection Agency minimum risk pesticide. Previous studies have shown various concentrations of geraniol repel or kill mosquitoes; however, geraniol might cause allergic contact dermatitis in humans or animals. We tested a commercially available 2% aqueous solution of geraniol on ponies as a mosquito repellent. Five trials were conducted on ponies treated with a 60-ml aerosol mist (30 ml per side) of 2% geraniol or as untreated controls. Animals were observed 3 h postapplication to check for skin irritation. Aedes aegypti, in feeding tubes, were held on the ponies for 7 min. The average percent of biting on control animals was 56%, with a range of 16-90%, and the average for the treatments was 13%, with a range of 0-86%. Based on statistical models, there was no significant difference (P = 0.081) in the percent bites between treated and untreated animals after 3 h. Based on our data, 2% geraniol was not an adequate mosquito repellent for horses. We did not observe any skin irritation on the animals treated with 2% geraniol.

Is There Evidence that Methyl Heptine Carbonate Causes Allergic Contact Dermatitis?

The fragrance material methyl heptine carbonate has been cited as a moderately frequent cause of cosmetics-related allergic contact dermatitis. A review of the literature shows that when the underlying clinical data are analyzed, there is only one published case where a possible causal link to a cosmetic product has been established. Predictive tests in a computational model, in animal systems, and in volunteers have demonstrated a significant sensitization potential for this substance but reports of clinical cases of allergy are rare with no new reports appearing in the last two decades. The infrequence of reported cases of allergy may be linked to risk management procedures put in place by the International Fragrance Association (IFRA) more than 20 years ago.