An Unusual Case of Contact Dermatitis

The document reports the first case of allergic contact dermatitis caused by a low-level light therapy (LLLT) cap used for the treatment of androgenetic alopecia (AGA). A 65-year-old male patient with a history of AGA and multiple hair transplants presented with acute psoriasiform contact dermatitis on his forehead and scalp after using an LLLT cap lined with plastic, rubber, and an interior metal probe. Patch testing revealed positive reactions to several allergens, including dimethylol dihydroxyethyleneurea (DMDE), which was suspected to be in the fabric of the cap. The patient's skin condition improved significantly after he stopped using the cap and continued to improve with the use of topical steroids. The case highlights the potential for allergic reactions to components of LLLT devices, despite their general safety and the absence of serious adverse events reported in a previous study with 269 subjects. The diagnosis of allergic contact dermatitis to DMDE was confirmed based on the clinical presentation, positive patch test results, and resolution of symptoms upon discontinuation of the cap.