Mechanistic in vivo studies of secondary skin-to-skin peanut allergen transfer to determine the impact of hand washing in reducing the risk of cutaneous sensitization.

BACKGROUND: In Europe, 1-2% of children are diagnosed with a peanut allergy. Atopic dermatitis (AD) is a significant risk factor for food allergy development, with cutaneous allergen exposure playing a causative role in allergic sensitization, particularly in early childhood.

OBJECTIVES: To investigate the primary and secondary skin-to-skin transfer of peanut proteins and the impact of hand washing in reducing allergen transfer.

METHODS: Primary transfer and secondary skin-to-skin transfer of fluorescently labelled peanut proteins was determined with and without hand washing, using two commonly used soaps containing ionic or nonionic surfactants, in 11 healthy volunteers. Tape stripping and fluorescence quantification of the peanut proteins on the tapes were used to analyse skin transfer. The depth of peanut protein deposition in the skin was determined in situ by confocal laser scanning microscopy.

RESULTS: Over 50% of the peanut proteins penetrated the upper horn layer during primary transfer, with aqueous solutions being significantly more effective [mean (SD) 70.5% (7.6)] compared with glycerol [mean (SD) 53.8% (11.2); P ≤ 0.001]. Approximately 10% of the proteins underwent secondary transfer, with higher values observed for glycerol than for water (9.8% vs. 7.8%). This was related to the amount of peanut applied after primary transfer (P ≤ 0.05 for water; P ≤ 0.01 for glycerol). Hand washing removed up to 90% of the applied peanut proteins. For proteins dissolved in water, nonionic soap was more effective (87.6%) than anionic soap (63.7%) in removing the applied peanut proteins from the palm (P ≤ 0.01). When proteins were dissolved in glycerol, both soaps were similarly effective in clearing protein contamination from the palm (approximately 97-99%; P ≤ 0.01).

CONCLUSIONS: We demonstrate the rapid contamination of hands with allergenic peanut protein and the potential for skin-to-skin transfer. Hand hygiene prevented allergen transmission by up to 90%. Soaps based on nonionic surfactants were more robust to external factors than classical anionic soaps, and this may be particularly important for infants with AD.

© The Author(s) 2025. Published by Oxford University Press on behalf of British Association of Dermatologists.

PMID: 40827861