High Prevalence of Contact Hypersensitivity to Metals and Preservatives in Chinese Patients with Atopic Dermatitis
Atopic dermatitis (AD) is a chronic inflammatory skin condition characterized by recurrent dermatitis and intense itching. Most patients with AD have a personal or family history of atopic diseases, such as asthma or allergic rhinitis. While allergies to airborne and food allergens are well-documented features of AD, there has been limited research on contact sensitization in these patients. This raises the question of whether patch testing should be more widely used as a screening tool in AD patients to identify hidden allergies that may exacerbate their symptoms. This study aimed to compare patch test results between patients with AD and non-AD patients, including those with facial dermatitis, eczema, psoriasis, pruritus, and urticaria, as well as healthy individuals.
The study involved 988 patients who underwent patch testing. The median age of the participants was 36 years, ranging from 7 to 90 years old. Among these, 10.3% were diagnosed with AD. The diagnosis of AD was established using the Chinese criteria, and all patients were assessed for atopic status, including dermatitis, asthma, and allergic rhinitis. Patch testing was performed using the Chinese Baseline Series and IQ chambers from Chemotechnique Diagnostics in Malmö, Sweden. The patches were applied to the upper back for 48 hours, and results were recorded on day 2 and day 7 according to the International Contact Dermatitis Research Group guidelines.
The study found that 78.4% of AD patients tested positive for at least one allergen, which was significantly higher than the 66.8% positivity rate in non-AD patients. The top three allergens in AD patients were nickel (II) sulfate hexahydrate (33.3%), cobalt (II) chloride hexahydrate, and methylisothiazolinone. In non-AD patients, the most common allergens were methylisothiazolinone (15.7%), nickel (II) sulfate hexahydrate (11.4%), and mercapto mix (10.8%). Notably, 33.3% of AD patients had a positive response to nickel sulfate, which was significantly higher than the 11.4% positivity rate in non-AD patients. Similarly, 19.6% of AD patients were positive for cobalt chloride, compared to 9.3% of non-AD patients. The response to methylisothiazolinone was 22.5% in AD patients and 15.7% in non-AD patients, though this difference was not statistically significant.
Genetic susceptibility plays a crucial role in AD, with null mutations in the filaggrin (FLG) gene identified as strong genetic risk factors. The exact mechanism by which FLG interacts with nickel in the stratum corneum remains unclear, but it has been speculated that the histidine-rich polypeptide FLG chelates nickel in the epidermis, creating a reservoir that prevents free ions from permeating the skin and inducing sensitization. This mechanism may explain why AD predisposes individuals to reactions to other metallic allergens, such as cobalt.
Cobalt chloride was identified as a significant allergen in AD patients, with 19.6% of AD patients testing positive compared to 9.3% of non-AD patients. Cobalt was named the allergen of the year in 2016, and since then, its potential exposure and associated contact allergy have garnered increased attention. While cobalt allergy is often linked to concomitant exposure to nickel, it is increasingly recognized as an independent sensitizer. Sources of cobalt exposure are varied and can include furniture, laptop computers, cosmetics, jewelry, buttons, zippers, snaps, and leather shoes. In pediatric patients with AD, 50% of patch testing was related to metals, highlighting the importance of identifying and managing metal allergies in this population.
Cobalt chloride is a strong sensitizer and can be challenging to use in patch testing due to the potential for irritant or doubtful reactions. However, exposure to irritants and a history of irritant dermatitis may also be risk factors for the development of allergic contact dermatitis. Irritants can compromise the skin barrier, allowing allergens to interact with the immune system. This suggests that the association between AD and positive patch test results reported in this study may indicate a relationship between AD and cobalt chloride, though further research is needed to confirm this.
The study also highlighted the potential role of preservatives in contact hypersensitivity among AD patients. The frequent use of emollients by Chinese AD patients may contribute to an increased risk of contact hypersensitivity to preservatives. Parabens, including methyl, ethyl, propyl, and butyl parabens, are the most common preservatives used in creams, lotions, and other products. As AD patients often use these products, they may be at higher risk for developing preservative allergies.
In conclusion, this study underscores the high prevalence of contact hypersensitivity to metals and preservatives in Chinese patients with AD. The findings suggest that patch testing could be a valuable tool in identifying hidden allergies that may exacerbate AD symptoms. The significant positivity rates for nickel and cobalt in AD patients highlight the importance of considering metal allergies in the management of AD. Additionally, the potential role of preservatives in contact hypersensitivity among AD patients warrants further investigation. These insights can help improve the diagnosis and treatment of AD, ultimately enhancing patient outcomes.
doi.org/10.1097/CM9.0000000000000526
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