Photopatch testing in Asians: a 5-year experience in Singapore

Background Photopatch testing is important for diagnosing photoallergic contact dermatitis. We aimed to evaluate the use of photopatch test at the National Skin Centre, Singapore. Methods All patients who had photopatch tests done between 2007 and 2011 at the National Skin Centre were included. Results Twenty-two patients were included. The mean age was 40.2. Female:male ratio was 3.4. The ethnic groups were Chinese (68%), Malay (4%), Indian (14%) and others (14%). Ten out of 22 patients (45.5%) had a positive photopatch test. There were 20 positive photopatch test reactions found in these 10 patients, and all 20 positive reactions were of current relevance. The frequencies of the positive photopatch test reactions were 2-hydroxy-4-methoxybenzophenone (oxybenzone) (n=6), 2-hydroxymethoxymethylbenzophenone (mexenone) (n=3), 2-ethylhexyl-4-dimethylaminobenzoate (n=1), ketoprofen gel (n=1) and the patient's own product (n=9). Conclusions Our study suggests that sunscreen is the most common photoallergen to date as opposed to musk ambrette, which was the most common photoallergen in our earlier study in 19911993. This finding is similar to the recent European Multicentre Photopatch Test Study.