Dear members,

Summarised below are four recent publications regarding findings from patch testing in older patients, photopatch testing and observations on testing to DPG as well as a case report on ACD to hydroquinone.

Hydroquinone Allergic Contact Dermatitis: Widening the Potential Dangers of Black Henna Tattoos.

Bridgewater K and Stone NM, Contact Dermatitis. 2026: 1–3

This case report of hydroquinone contact allergy (used in a combination cream with tretinoin 0.025% and fluocinolone acetonide 0.01% for melasma, purchased through an online personalised prescription skin service) in a patient with a history of severe p-phenylenediamine (PPD) allergy. Patch testing was positive to both hydroquinone and tert-butylhydroquinone as well as strong positive to the product itself. The authors raised the possibility of cross-reactivity between hydroquinone and PPD via the shared metabolite benzoquinone. As access to hydroquinone through online skincare services increases, dermatologists may wish to enquire about previous black henna tattoo or hair dye reactions before prescribing hydroquinone-containing products.

Forgotten Skin: What do our geriatric patch test findings reveal?

Gorgulu Akin B, Kalkan F, Maden S, Bayrak Durmaz M S, Ozdel Ozturk B, Burak Kursun M, & Soyyiğit S. Allergologia Et Immunopathologia. 2026. 54(3), 87-95.

This retrospective patch test study analysed 128 patients aged ≥65 years patch tested with the European Standard Series (ESS). Only 22 patients were ≥75 years of age. Preservatives, fragrances and propolis were the most common contact allergens identified. In patients aged 65–74 years, propolis (20%), fragrance mix I (17%), methyldibromo glutaronitrile (16%) and Peru balsam (15.1%) predominated, whereas MCI/MI (22.7%) was the leading allergen, followed by MI, propolis, and textile dye mix (all 13.6%) in those aged ≥75 years. In both groups, the hands were the most frequent site for allergic contact dermatitis. The prevalence of propolis was postulated to be due to exposure from topical formulations. Positive reactions were less frequent and generally weaker in the older age group, supporting the concept of immunosenescence and diminished T cell responsiveness in advanced age. The findings highlight the continued value of patch testing in older adults and suggest that allergen profiles differ with advancing age.

Prospective Multi-Centre Photopatch Test Study of Photoallergy to Sunscreens and NSAIDs in Europe.

Ralph N, Goossens A, Carrascosa JM, Goncalo M, Wulf HC, Calzavara-Pinton PG, Rhodes LE, Wilkinson M, Bourke J, Eadie E, Moore E, Christou E, Ibbotson SH. Br J Dermatol. 2026 Mar 28:ljag085. doi: 10.1093/bjd/ljag085.

In this prospective multicentre European study, photopatch testing identified photoallergic reactions to sunscreen chemicals in 10% of patients and to topical NSAIDs in 9%. The most common photoallergens were ketoprofen, promethazine, avobenzone (butyl methoxydibenzoylmethane), oxybenzone (benzophenone-3) and etofenamate. No positive photoallergic ACD was detected in patients with chronic actinic dermatitis (CAD). A key methodological finding was that a 24-hour occlusion period before UVA irradiation missed 53% of sunscreen photoallergic reactions and 36% of NSAID photoallergic reactions compared with a 48-hour occlusion. Whilst the topical photoallergens seem relatively stable in nature, the authors recommend a 48-hour occlusion period prior to irradiation to optimise the diagnostic yield of photopatch testing.

Allergic Contact Dermatitis to 1,3-Diphenylguanidine Over a 23-Year Period: Recent Cases Involve Sterile Polyisoprene Gloves.

Brasher TR, Palmer A, Nixon RL. Contact Dermatitis. 2026 May 8. doi: 10.1111/cod.70178. Epub ahead of print. PMID: 42099181.

In this retrospective audit of 2675 patients patch tested between 2002 and 2024, 1.9% had positive reactions to 1,3-diphenylguanidine (DPG), a rubber vulcanisation accelerator. Of these, 31 (62%) were diagnosed with clinically relevant allergic contact dermatitis (ACD). Patients with DPG ACD were more likely to be male, aged over 40 years, have occupationally related dermatitis, and present with hand involvement. Gloves and footwear were the most common exposure sources, with over half of the relevant cases linked to gloves. Notably, the four most recent cases involved healthcare workers exposed to sterile polyisoprene gloves, presenting with predominantly dorsal hand dermatitis and paronychia. The authors conclude that DPG remains an important cause of occupational ACD, particularly in healthcare settings, and highlight sterile polyisoprene gloves as a potential source of exposure that should be considered during patch testing and workplace investigations.