Peanut Oil Sensitisation

Peanut oil sensitisation is the hypothesis that infants can become allergic to peanut through the skin, especially when peanut-containing products are applied to inflamed, eczematous skin. The key evidence is Lack et al., New England Journal of Medicine 2003, which analysed the ALSPAC birth cohort of 13,971 preschool children in the Bristol area. Forty-nine children had a history of peanut allergy, and peanut challenge confirmed it in 23 of the 36 tested (Oral Food Challenge). There was no evidence that the mother’s diet in pregnancy sensitised the children, and peanut IgE was undetectable in cord blood. Peanut allergy was independently associated with the use of skin preparations containing peanut oil (OR 6.8, 95% CI 1.4–32.9). It was also associated with oozing, crusted rash (OR 5.2, 2.7–10.2), rash over joints and skin creases (OR 2.6), and soy milk or soy formula (OR 2.6). The authors concluded that “sensitization to peanut protein may occur in children through the application of peanut oil to inflamed skin.”

Peanut Oil Sensitisation [causes] Food Allergy ALSPAC [supports] Peanut Oil Sensitisation Atopic Dermatitis [worsens] Peanut Oil Sensitisation

Strength and limits. This is a single observational cohort, and the exposure data came from parent interviews. The very wide confidence interval (1.4–32.9) shows that few children were exposed, so evidence_strength: alleged stands. Even so, the finding fits later mechanistic and trial evidence: the Dual-Allergen Exposure Hypothesis (skin exposure sensitises, oral exposure tolerises) and the LEAP Trial, in which early peanut eating cut peanut allergy by about 86% in skin-test-negative infants with severe eczema or egg allergy. The soy association may reflect cross-sensitisation through shared epitopes, since peanut is a legume (Lack 2003). The same skin-route concern is applied by analogy to Tree Nut Allergy and to Almond Oil (Guillet 2000).

Peanut Oil Sensitisation [supports] Dual-Allergen Exposure Hypothesis LEAP Trial [opposes] Peanut Oil Sensitisation

Arachis oil in UK products and medicines. Peanut oil is listed as Arachis Oil (INCI/BP name Arachis hypogaea oil) in medicines and cosmetics, and many parents and even pharmacy staff do not recognise the name. Refined arachis oil is used as a carrier or absorption aid. UK examples include Zinc and castor oil ointment BP (Thornton & Ross) and Naseptin nasal cream (Pharmaceutical Journal 2021). New Zealand’s regulator also lists Cerumol ear drops, Polytar liquid and zinc and castor oil ointment (Medsafe 2012). Formulations change, so always check the current leaflet. Under the EMA excipient guideline (2003, annex updated 2019), the product information and leaflet of any medicine containing arachis oil must state that it is contraindicated in known peanut or soya allergy. The European Pharmacopoeia does not require testing for residual protein, so trace peanut protein may remain. In 2021 a peanut-allergic child at Sheffield Children’s was dispensed Naseptin after the dispenser skipped the “Contains arachis oil” label because they did not know what it meant. The trust then reworded the label to “Warning: contains arachis oil. Do not use if you have a peanut allergy”. Medsafe notes that medicinal peanut oil is highly refined, with most or all protein removed, but still advises caution because tiny exposures can trigger reactions.

Arachis Oil [part-of] Peanut Oil Sensitisation Arachis Oil [triggers] Food Allergy

Nut-based oils on eczema skin

Do not apply peanut (arachis) oil, nut oils or creams containing them to a baby’s or toddler’s eczema, particularly on broken, oozing skin, and do not use nut-oil massage blends. Check labels for “arachis oil”, “Arachis hypogaea” and tree-nut oils (sweet almond = Prunus amygdalus dulcis). This applies to emollients, nappy-area zinc and castor oil ointments, ear drops and “natural” balms. For children already allergic to peanut or soya, ask the pharmacist to check every prescribed or bought product.

Conflict on refined oil. Refined arachis oil is thought to carry little or no protein, and the Pharmaceutical Journal cites Hourihane et al. 1997, a small double-blind challenge in peanut-allergic adults, as suggesting a low risk of reaction. Lack 2003, however, could not tell refined from crude oil in the products parents reported, so the dose of protein needed for skin sensitisation (as opposed to triggering a reaction in someone already allergic) is unknown.

Conflict: [Pharmaceutical Journal / Hourihane, 2021/1997] says refined arachis oil carries low allergic risk to the already-allergic. [Lack, NEJM 2003] links peanut-oil skin preparations with new peanut sensitisation (OR 6.8), without distinguishing refined oil. Unresolved — add to open_questions.

Connections

• Food Allergy — skin route to peanut allergy, source: Lack 2003
• Dual-Allergen Exposure Hypothesis — supporting cohort evidence, source: Lack 2003
• Coconut Oil — nut-oil warning on natural-oil notes, source: Lack 2003
• Sunflower Seed Oil — nut-oil blend hazard, source: Lack 2003
• Olive Oil — nut-oil blend hazard, source: Lack 2003
• LEAP Trial — oral peanut early prevents allergy that skin exposure promotes, source: Du Toit 2015
• Shea Butter — tree-nut butter; refined form has no detectable protein, raw form untested, source: FARRP 2018
• Tree Nut Allergy — same skin-sensitisation concern for nut-derived products, source: Lack 2003
• Almond Oil — parallel case: almond oil sensitised AD infant, source: Guillet 2000
• Arachis Oil — UK/EU label name; EMA contraindication in peanut/soya allergy, source: Pharm J 2021
• ALSPAC — source cohort (13,971 children), source: Lack 2003
• Oral Food Challenge — peanut allergy challenge-confirmed in 23/36, source: Lack 2003