HX17 The fortunate side effect: serendipity and therapeutic innovation in dermatology

Abstract

Since the earliest days of dermatology, therapeutic innovation has frequently arisen from careful clinical observation, particularly the recognition of unexpected drug effects. Such serendipitous discoveries have repeatedly reshaped dermatological practice, leading to the repurposing of existing agents for cutaneous disease. In the 19th century, coal tar, an industrial by-product initially employed as an antiseptic, was noted to improve psoriatic plaques and subsequently became a mainstay topical therapy for hyperkeratotic dermatoses. Around the same period, arsenic-based compounds, most notably Fowler’s solution, prescribed for malaria, syphilis and anaemia, were observed to reduce scaling and inflammation in psoriasis, representing one of dermatology’s earliest systemic treatments. The twentieth century saw further paradigm-shifting examples of drug repurposing. Minoxidil, developed as an antihypertensive agent, was associated with unexpected hypertrichosis, leading to its widespread use in androgenetic alopecia. Isotretinoin, initially synthesized in the 1970s for disorders of keratinization such as ichthyosis, was observed to dramatically improve acne in trial participants with coexistent disease, transforming the management of severe acne. Similarly, antimalarials were incidentally found to improve cutaneous lupus erythematosus in soldiers receiving quinacrine prophylaxis during the Second World War, with hydroxychloroquine later emerging as the preferred agent due to its improved safety profile. More recently, propranolol has exemplified the power of clinical observation in modern dermatology. It was initially used for cardiovascular indications, but its dramatic efficacy in inducing involution of infantile haemangiomas was discovered serendipitously and rapidly translated into practice. Likewise, Janus kinase inhibitors were observed to induce hair regrowth in patients treated for inflammatory arthritis, catalysing the development of targeted therapies for alopecia areata. Collectively, these examples illustrate that while chance observations may initiate discovery, it is rigorous clinical insight, systematic investigation and reproducibility that transform serendipity into meaningful therapeutic advances. They highlight dermatology’s unique capacity for innovation and the continued importance of vigilance in clinical practice.