The authors dismissed the diagnosis of carboxymethylcellulose (CMC) excipient allergy based on negative skin tests (skin prick [SPT] and intradermal tests [IDT]) and oral CMC provocation test. However, CMC is known to be poorly absorbed via the gastrointestinal tract and is tolerated by patients allergic to systemically administered CMC [23]. As the predictive value of CMC skin tests remains to be elucidated, we believe that immediate hypersensitivity to CMC cannot be excluded based on a negative oral provocation test alone.

Furthermore, we would also like to highlight that the “Classification of corticosteroids” (quoted from Baeck et al.) was based on sensitization profiles derived from patch testing, i.e., delayed hypersensitivity, rather than immediate hypersensitivity [45]. To avoid confusion, it is important to note that this classification is unlikely to be useful when evaluating patients presenting with immediate reactions [5]. In our experience, we have not identified any consistent patterns of cross-reactivity in immediate hypersensitivity. When searching for suitable alternatives, we would instead advocate an individualized and comprehensive approach based on our previously published algorithm [6].

In our recently published series [6], we recognised that the majority of patients with immediate reactions (after complete evaluations) were actually allergic to the excipients rather than the corticosteroid. We also identified the use of preservative free Carmellose eye drops 1% (Moorfields Pharmaceuticals, London, UK) as a readily available and reliable source of CMC for skin testing.

Therefore, based on our algorithm, we would suggest performing SPT and IDT with CMC were performed with preservative free Carmellose eye drops 1% (Moorfields Pharmaceuticals) with undiluted and 1:10 dilution, respectively. This concentration has been proven to be nonirritative in healthy controls, and we have successfully identified CMC allergy in numerous proven cases using this approach [6]. Following negative skin tests, we would strongly recommend further testing with excipient-free triamcinolone instead to more accurately differentiate between triamcinolone and CMC allergy. Prior to the completion of comprehensive testing, the patient should continue to avoid all corticosteroid and excipient containing compounds.

Immediate hypersensitivity to corticosteroids is often overdiagnosed, leading to unnecessary avoidance or potentially dangerous exposure to other medications containing similar excipients. True allergy to corticosteroid is extremely rare and we emphasize that patients should only be labelled after excipient allergy has been confidently excluded following comprehensive testing.