Ideal proportion of the population to be patch tested: How many should we be doing?

BACKGROUND: How many patients should we be patch testing? A previous study suggested that the minimum proportion of a population to be patch tested for allergic contact dermatitis was 1:700 annually. OBJECTIVES: To evaluate if the current minimum rate for patch testing has changed over the 20 years since the previous study in order to maximize the value. METHODS: In cooperation with the British Society for Cutaneous Allergy, a proforma for collation of retrospective data between January 2015 and December 2017 was sent to patch-test centers in the United Kingdom (UK) and the Republic of Ireland (ROI). The number of positive tests was analyzed against the proportion of population tested to see what proportion of the population would yield the greatest number of positive results. RESULTS: Responses from 11 centers showed that the minimum number needed to patch test had increased to 1:550 per head of population per year using the current criteria. CONCLUSIONS: In agreement with previous studies, we should be patch testing more people than we are. We could reduce the threshold for referral of patients we patch test to derive the most benefit from this investigation.

Contact allergy to essential oils cannot always be predicted from allergy to fragrance markers in the baseline series.

BACKGROUND: Essential oils are fragrance substances that are labelled on cosmetic products by their INCI names, potentially confusing consumers. OBJECTIVES: To establish whether contact allergy to essential oils might be missed if not specifically tested for. METHODS: We tested 471 patients with 14 essential oils and 2104 patients with Melaleuca alternifolia oil between January 2008 and June 2014. All patients were tested with fragrance mix I, fragrance mix II, hydroxyisohexyl 3-cyclohexene carboxaldehyde, and Myroxylon pereirae. Three hundred and twenty-six patients were tested with hydroperoxides of limonene and linalool. RESULTS: Thirty-four patients had a +/++/+++ reaction to at least one essential oil. Eleven had no reaction to any of the six marker fragrance substances. Thus, 4 of 11 positive reactions to M. alternifolia oil, 2 of 7 reactions to Cymbopogon flexuosus oil, 1 of 5 reactions to Cananga odorata oil, 3 of 4 reactions to Santalum album oil and 2 of 3 reactions to Mentha piperita oil would have been missed without individual testing. CONCLUSION: A small number of patients who are allergic to essential oils could be missed if these are not specifically tested. Labelling by INCI names means that exposure may not be obvious. Careful inspection of so-called 'natural' products and targeted testing is recommended.

Patch testing is a useful investigation in children with eczema.

BACKGROUND: Allergic contact dermatitis in children is less recognized than in adults. However, recently, allergic contact dermatitis has started to attract more interest as a cause of or contributor to eczema in children, and patch testing has been gaining in recognition as a useful diagnostic tool in this group. OBJECTIVES: The aim of this analysis was to investigate the results of patch testing of selected children with eczema of various types (mostly atopic dermatitis) attending the Sheffield Children's Hospital, and to assess potential allergens that might elicit allergic contact dermatitis. PATIENTS AND METHODS: We analysed retrospectively the patch test results in 110 children aged between 2 and 18 years, referred to a contact dermatitis clinic between April 2002 and December 2008. We looked at the percentages of relevant positive reactions in boys and girls, by age groups, and recorded the outcome of treatment following patch testing. RESULTS: One or more positive allergic reactions of current or past relevance was found in 48/110 children (44%; 29 females and 19 males). There were 94 allergy-positive patch test reactions in 110 patients: 81 had a reaction of current or past relevance, 12 had a reaction of unknown relevance, and 1 had reaction that was a cross-reaction. The commonest allergens with present or past relevance were medicaments, plant allergens, house dust mite, nickel, Amerchol® L101 (a lanolin derivative), and 2-bromo-2-nitropropane-1,3-diol. However, finding a positive allergen was not associated with a better clinical outcome. CONCLUSIONS: We have shown that patch testing can identify relevant allergens in 44% of children with eczema. The commonest relevant allergens were medicament allergens, plant allergens, house dust mite, nickel, Amerchol® L101, and 2-bromo-2-nitropropane-1,3-diol. Patch testing can be performed in children as young as 2 years with the proper preparation.

Contact allergy to topical medicaments becomes more common with advancing age: an age-stratified study.

Eczema is common in the elderly people who often use topical medicaments. Previous studies in the elderly people have noted allergic positive patch tests in between 43% and 64% of those tested. We set out to assess whether medicament contact allergies are more common in elderly patients. We undertook a retrospective age-stratified study of all patients patch tested at the Royal Hallamshire Hospital, Sheffield, between January 1994 and July 2005. We confirmed that contact allergy to topical medicaments is more common in those aged more than 70 years compared with the younger age groups. There was no sex difference. The commonest problematic allergen types found in medicaments were fragrances and preservatives. The most frequent individual allergens were fragrance mix, Myroxylon pereirae, lanolins, local anaesthetic agents, neomycin and gentamicin, and tixocortol pivolate. The pattern of medicament contact allergens was similar to that of the younger age groups except that multiple allergic positives were more frequent and sensitivities to local anaesthetics and Myroxylon pereirae were proportionally more common. Elderly patients were more likely to have multiple contact allergies than the younger ones. Care needs to be taken when prescribing topical medicaments to elderly patients with eczema, especially for preparations that contain perfumes, lanolins, and local anaesthetics.

10 years' experience of patch testing with a shoe series in 230 patients: which allergens are important?

Over a 10-year period, 230 patients with foot dermatitis were patch tested to a shoe series of allergens. About 54 (23%) had relevant allergic positive reactions to one or more allergens. The commonest relevant allergens groups were, in order, chromate, medicaments, rubber chemicals, dyes and cosmetic constituents, with the most frequent individual allergens being chromate (4%), neomycin (3%), rubber chemicals (> 3%), paraphenylenediamine (2%) and tixocortyl pivolate (2%). Some allergens previously thought to be important, e.g. certain plastic and adhesive chemicals, did not show any positives over the period of study. In addition, para-tertiary butyl phenol formaldehyde resin was a relatively unimportant allergen in this series. The main practical points to emerge from this study are that, in patients with foot dermatitis, chromate is still the principal allergen, and that medicament and cosmetic allergens may be prominent.