Immediate and Delayed Hypersensitivity Testing to Grasses in Singapore: A 24-Year Retrospective Review

Grass exposure is common in Singapore, particularly among young men undergoing compulsory military service, and often prompts evaluation for suspected grass allergy. While most reactions are irritant, the contemporary prevalence of true grass hypersensitivity is unclear.

To update the epidemiology, clinical features and diagnostic outcomes of patients evaluated for suspected grass-induced dermatitis or urticaria in Singapore.

We performed a retrospective review of patients seen at the Contact and Occupational Dermatoses Clinic, National Skin Centre, from January 2000 to December 2023 who underwent patch testing and/or skin prick testing for suspected grass-related reactions. Demographic data, clinical morphology and test outcomes were analysed descriptively.

A total of 191 patients were included (mean age 20.6 years; 97% male), most referred for military-related assessment. Skin prick testing to grass was performed in 83%, with positive results in 3%. Patch testing was performed in 97%, with positive reactions in 5%. Most patients presented with eczematous or urticarial eruptions, yet confirmed immunologic grass hypersensitivity was uncommon. Sensitisation to house dust mites was frequent but did not correlate with grass allergy.

True grass allergy is rare despite high exposure. Objective testing is crucial to differentiate hypersensitivity from irritant or non-allergic reactions, particularly when diagnoses have significant occupational consequences.