The former Nickel Directive was introduced in EU in 1994 limiting the release of nickel from items intended for prolonged contact with skin. The nickel regulation entered into full force in 2001 and became a part of REACH (the EU chemicals regulation) in 2009. Since then the prevalence of nickel allergy has declined in some countries, but not in others, following the implementation. Young individuals still become allergic to nickel (2, 3) and a high prevalence of nickel allergy, exceeding 10%, is seen among young women (below 30 years) in the general population.

The EU nickel regulation has been changing over time. The present limits of nickel release for metallic items intended for direct and prolonged contact with the skin is <0.5 μg/cm2/week and <0.2 μg/cm2/week for any post assemblies inserted into pierced holes. In 2014, EU defined prolonged contact with the skin as: at least 30 minutes on one or more occasions within two weeks for items with continuous skin contact, or to at least 10 minutes on three or more occasions within two weeks (7).

The overall objective is to evaluate how well the EU nickel regulation protects individuals against developing nickel dermatitis. More specifically we will:

1. Study the penetration of nickel in normal and irritated skin after short repeated skin exposure under controlled temperature in nickel sensitized patients and in healthy controls
2. Reveal the potential of short repeated nickel skin exposure on normal and irritated skin to elicit dermatitis, during controlled climate factors in nickel sensitized patients and controls using the time restrictions of the definition of prolonged skin contact in the nickel regulation.

For patients with nickel allergy:

Inclusion Criteria:

• Positive patch test to nickel sulphate 5% pet. according to European society of contact dermatitis(ESCD) guidelines within the last 5 years at the Department of Dermatology and Allergy, Gentofte Hospital.
• Age 18-75 years.

Exclusion Criteria:

• Active eczema in test areas
• Generalized eczema
• Scar tissue in test areas.
• Pregnancy or breast feeding
• Treatment with topical corticosteroids or other immune-suppressants on/near test areas within four weeks prior to study start
• Systemic immunomodulatory* treatment within 4 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 *Systemic immunomodulatory treatment is drugs taken orally or by injection that modify the response of the immune system by increasing (immunostimulators) or decreasing (immunosuppressives) the production of serum antibodies

For Healthy volunteers:

Inclusion Criteria:

• Negative patch test result to nickel sulphate 5% pet. according to ESCD guidelines (48) at the Department of Dermatology and Allergy, Gentofte Hospital
• Age 18-75 years.

Exclusion Criteria:

• History of contact allergy
• Generalized eczema
• Scar tissue in test areas.
• Pregnancy or breast feeding
• Treatment with topical corticosteroids or other immune-suppressants on/near test areas within four weeks prior to study start
• Systemic immunomodulatory 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