Linalool is currently one of the most used fragrance substances in cosmetic and household products. Previous studies report a high prevalence (5.9-11.7%) of contact allergy to hydroperoxides of linalool (Lin-OOH)1.0% in pet. among patch tested patients. The optimal test concentration of Lin-OOH in patch tests is not known and requires further investigation. It is of great importance to establish the optimal test concentration and elicitation threshold of Lin-OOH to improve diagnosis and prevent development of Allergic Contact Dermatitis (ACD).

We want to mimic real-life exposure to Lin-OOH, by conducting a ROAT (Repeated Open Application Test) study, on 40 adult participants (20 patients with confirmed contact allergy to Lin-OOH, and 20 healthy participants) to low doses of Lin-OOH using a simulated "perfume", during a maximum of 21 days of exposure.

With this knowledge, we aim to:

1. Establish the optimal patch test concentration to diagnose ACD to Lin-OOH
2. In case of confirmed contact allergy, examine the threshold value for the development of ACD upon daily exposure to a simulated leave-on cosmetic product

Allergic participants:

1. Inclusion criteria

   • Positive (at least one reading) or doubtful patch test (at least two readings) result to hydroperoxides of Linalool within the last ten years
   • Aged 18 years or older
   • Received written and verbal information of the study
   • Signed written consent form

2. Exclusion criteria

   • Active eczema in test areas (volar forearms)
   • Pregnancy or breast feeding
   • Treatment with topical corticosteroids or other immune suppressants on/near test areas within two weeks prior to study start
   • Systemic immune-suppressant treatment within seven days prior to study start
   • UV exposure of test areas within three weeks prior to study start
   • Unable to cooperate or communicate with the investigators

Healthy controls:

1. Inclusion criteria

   • Aged 18 years or older
   • Received written and verbal information of the study
   • Signed written consent form

2. Exclusion criteria

   • Known or possible contact allergy to hydroperoxides of Linalool
   • Known contact allergy to other fragrance allergens
   • Active eczema or other known relevant skin diseases
   • Pregnancy or breast feeding
   • Treatment with topical corticosteroids or other immune suppressants on/near test areas within four weeks prior to study start.
   • Systemic immune-suppressant treatment within four weeks prior to study start.
   • UV exposure of test areas within three weeks prior to study start.
   • Participation in other clinical studies within four weeks prior to study start.
   • Unable to cooperate or communicate with the investigators.