What’s new in contact dermatitis?

Tools to help diagnose and treat contact dermatitis are on the way.

Allergic contact dermatitis is an itchy, red and scaly skin rash caused by an allergic reaction to a substance contacting the skin. Allergic contact dermatitis is diagnosed by patch testing.

Associate Professor Rosemary Nixon AM and her team at the Skin Health Institute in Victoria have performed allergen patch testing on thousands of patients. Speaking to delegates at the Annual Scientific Meeting of the Australasian College of Dermatologists in Sydney earlier this year, Professor Nixon discussed the results of a review of the most commonly detected allergens between 2021 and 2022.

Fragrances, nickel, the preservatives methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), potassium dichromate and 4-phenylenediamine base (PPD, also known as permanent hair dye) were the most common allergens during this two-year span.

Over 160 fragrances have been reported to cause allergic contact dermatitis. Common fragrance allergens include hydroperoxides of limonene, hydroperoxides of linalool, fragrance mix I and II and Balsam of Peru. Perfumes, scented skincare products, shampoos, hand washes and essential oils (including those added to diffusers) are frequent sources of exposure.  

MCI/MI are preservatives present in many household products such as hand and body washes, shampoos, conditioners and wet wipes. MI allergy peaked in 2015 but has decreased following regulations limiting the concentration of MI allowed.

Potassium dichromate is most commonly found in wet cement or leather and is a common cause of skin problems among workers exposed to cement. PPD is a permanent hair dye and a common cause of allergic contact dermatitis in hairdressers, who are frequently exposed to these products.

Patch testing requires highly specialised training and is generally performed by dermatologists and their nurses. To address this ongoing need for training, the Occupational Dermatology Research and Education Centre team at the Skin Health Institute have developed a new course – the Patch Test Certificate.

The new course will help participants gain an understanding of patch testing while also improving their patch testing skills and knowledge, which are essential in performing safe and accurate patch testing. The course, which will be available by November 2023, will initially be offered to dermatology nurses and registrars, before being made available to qualified dermatologists.

The course will consist of independent study (reading lists as well as online lectures, demonstrations, case-based learning modules and quizzes) in addition to interactive teaching and lectures (either face to face or virtual). The cost of the course is yet to be announced.  

Once an allergen is identified with patch testing a key component of management is avoiding the culprit allergen, as there is no form of desensitisation for this allergy. Often patients will need to navigate complex ingredient lists in small fonts to find a suitable allergen-free product. These lists are often hard to understand and sometimes there are alternative names for the allergens, making it challenging and time consuming for both dermatologists and patients to find suitable products.

The CosMe app is a newly launched app developed by dermatologist Dr Francis Lai, designed to help patients find a suitable product compatible with their allergen profile. The CosMe app offers personalised recommendations based on users’ allergen profiles and includes 5000 products (with more products to be added in the future).

The CosMe app will help to educate patients and allow them to navigate the skincare landscape, which can be a minefield for those with allergies. It is also beneficial for dermatologists and will improve their ability to advise patients appropriately. The app is available for free via both the Apple and Google Play stores.