Lavender oil lacks natural protection against autoxidation, forming strong contact allergens on air exposure

Allergic contact dermatitis: epidemiology, molecular mechanisms, in vitro methods and regulatory aspects. Current knowledge assembled at an international workshop at BfR, Germany

Contact allergies are complex diseases, and one of the important challenges for public health and immunology. The German ‘Federal Institute for Risk Assessment’ hosted an ‘International Workshop on Contact Dermatitis’. The scope of the workshop was to discuss new discoveries and developments in the field of contact dermatitis. This included the epidemiology and molecular biology of contact allergy, as well as the development of new in vitro methods. Furthermore, it considered regulatory aspects aiming to reduce exposure to contact sensitisers. An estimated 15–20% of the general population suffers from contact allergy. Workplace exposure, age, sex, use of consumer products and genetic predispositions were identified as the most important risk factors. Research highlights included: advances in understanding of immune responses to contact sensitisers, the importance of autoxidation or enzyme-mediated oxidation for the activation of chemicals, the mechanisms through which hapten-protein conjugates are formed and the development of novel in vitro strategies for the identification of skin-sensitising chemicals. Dendritic cell cultures and structure-activity relationships are being developed to identify potential contact allergens. However, the local lymph node assay (LLNA) presently remains the validated method of choice for hazard identification and characterisation. At the workshop the use of the LLNA for regulatory purposes and for quantitative risk assessment was also discussed.

Linalool--a significant contact sensitizer after air exposure

BACKGROUND

Linalool is a widely used fragrance terpene. Pure linalool is not allergenic or a very weak allergen, but autoxidizes on air exposure and the oxidation products can cause contact allergy. Oxidized (ox.) linalool has previously been patch tested at a concentration of 2.0% in petrolatum (pet.) in 1511 patients, and 1.3% positive patch test reactions were observed.

OBJECTIVE

To investigate the optimal patch test concentration for detection of contact allergy to ox. linalool.

METHODS

Four concentrations of ox. linalool (2.0%, 4.0%, 6.0%, 11.0% pet.) were tested in 3418 consecutive dermatitis patients.

RESULTS

Ox. linalool 2.0%, 4.0%, 6.0%, and 11.0% pet. detected positive patch test reactions in 0.83%, 3.2%, 5.3%, and 7.2% of the tested patients, respectively. The doubtful reactions increased with rising concentrations but relatively less, giving 5.1%, 6.4%, and 7.3% doubtful reactions, respectively, for ox. linalool 4.0%, 6.0%, and 11.0% pet. Few irritative reactions were seen.

CONCLUSIONS

Raising the patch test concentration for ox. linalool gave a better detection of contact allergy, as many as 5-7% positive patch test reactions were detected. We suggest a patch test concentration of ox. linalool 6.0% pet. for future patch testing, giving a dose per unit area of 2.4 mg/cm(2) when 20 mg test substance is tested in small Finn Chambers.

Air oxidation increases skin irritation from fragrance terpenes

BACKGROUND

Linalool and limonene are common fragrance terpenes that autoxidize on air exposure. The pure compounds are not allergenic but their oxidation products can cause contact allergy. Little has been investigated regarding the irritancy of oxidized terpenes.

AIM

The aim of this study was to investigate the irritating effect of pure and oxidized R-limonene and linalool in concentration series and to study the MNIC (Maximum Non Irritant Concentration) of autoxidized linalool and limonene.

PATIENTS/METHODS

Patch testing was performed in dermatitis patients and controls with sequentially diluted concentrations of oxidized and non-oxidized linalool, and oxidized and non-oxidized R-limonene. Readings were made with visual assessment and using laser Doppler imaging.

RESULTS

The non-oxidized terpenes were non-irritating in all tested concentrations. Both linalool and especially R-limonene were more irritating after oxidation compared with the pure compounds. No difference in response was seen between dermatitis patients and controls.

CONCLUSION

Autoxidation of the fragrance terpenes linalool and R-limonene increases irritation. Oxidized linalool is less irritating than oxidized R-limonene. In this study, we found no advantages in using laser Doppler technique compared with visual assessment.