Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a delayed, T-cell-mediated (type IV) eczematous reaction to a substance that touches the skin. It usually appears 24–72 hours after contact (DermNet 2020), and Patch Testing is the only test that diagnoses it. In a child with Atopic Dermatitis it looks like an ordinary flare, so it is easy to miss. Clues are eczema that will not settle with proper treatment, or a rash in an unusual place such as the face, eyelids, hands, feet or nappy area. The old belief that young children rarely get ACD is wrong. Tam & Yu 2022 describe two peaks in early childhood, at 0–3 years and 6–7 years, and say that neonates and infants can be sensitised because their skin barrier is immature and they are exposed to many products. Botanical products are recognised causes: chamomile tea and Kamillosan cream have caused it (DermNet), and 2% of patients patch-tested in Reider 2001 reacted to marigold (Calendula).

Allergic Contact Dermatitis [relates] Atopic Dermatitis Patch Testing [defines] Allergic Contact Dermatitis Calendula [causes] Allergic Contact Dermatitis Chamomile [causes] Allergic Contact Dermatitis

How common it is in children with AD. In an Italian multicentre study, 432 children aged 0–14 were patch-tested in a row with the SIDAPA baseline series. Of these, 28.9% had at least one positive reaction. The rate was 36.9% in children with AD and 26.4% in those without, and 22.0% in the under-3s (Bonamonte 2022). Fragrance mixes and Methylisothiazolinone were positive more often in the AD group. In the US Pediatric Contact Dermatitis Registry, up to half of children with ACD had a previous AD diagnosis (Tam & Yu 2022). AD children were tested at younger ages and were more often positive to Lanolin, cocamidopropyl betaine, tixocortol pivalate (a marker for allergy to some Topical Corticosteroids) and parthenolide (a Compositae Allergy marker). These are all ingredients of the emollients and medicines these children use every day. The direction of the AD–ACD link is still argued over (see Conflict).

Atopic Dermatitis [relates] Allergic Contact Dermatitis Skin Barrier Dysfunction [causes] Allergic Contact Dermatitis Emollient Therapy [relates] Allergic Contact Dermatitis Lanolin [causes] Allergic Contact Dermatitis

Conflict: [Tam & Yu, Curr Allergy Asthma Rep, 2022] says patients with AD have “at least similar” ACD risk to non-AD patients, and that in the US registry AD children had lower rates of positive MCI/MI tests. [Bonamonte et al., Contact Dermatitis, 2022] found a higher patch-positive rate in AD children (36.9% vs 26.4%), with methylisothiazolinone and fragrance mixes more often positive in AD. Unresolved — add to open_questions.

Common allergens in young children. US paediatric data rank metals (nickel, cobalt) top, followed by fragrances (fragrance mix I/II, balsam of Peru), emollients and surfactants (propylene glycol, cocamidopropyl betaine, Lanolin), topical antibiotics (Neomycin, bacitracin) and preservatives (Methylisothiazolinone, MCI/MI, formaldehyde releasers) (Tam & Yu 2022, adapted from Neale 2021). The Italian ranking was nickel 10.2%, cobalt 6.7%, MI 3.7%, fragrance mix II 3.2% and fragrance mix I 2.1% (Bonamonte 2022). Lanolin, from sheep’s wool, sensitises 1.2–6.2% of children who are patch-tested. Neomycin has been a top paediatric allergen for decades, and its reactions can appear late, up to 3 weeks after testing. Plant allergens matter too: Compositae Allergy (Chamomile, Calendula), and linalool and limonene from Essential Oils, whose oxidised hydroperoxides are not covered by the standard fragrance mixes. Products sold as “hypoallergenic”, “for babies” or even “fragrance-free” have been found to contain fragrance, lanolin, cocamidopropyl betaine, propylene glycol and botanical extracts.

Fragrance Allergy [part-of] Allergic Contact Dermatitis Methylisothiazolinone [causes] Allergic Contact Dermatitis Neomycin [causes] Allergic Contact Dermatitis Essential Oils [causes] Allergic Contact Dermatitis Compositae Allergy [part-of] Allergic Contact Dermatitis

When to patch-test a toddler, and with what. Reasons to patch-test include suspected ACD, eczema in an atypical distribution (head and neck, hands and feet, nappy area), eczema that does not respond to treatment, and before starting systemic medicines (Tam & Yu 2022, Table 3). In 2018 a US expert workgroup published the Pediatric Baseline Series (Yu et al., Dermatitis): 38 allergens plus 2 of the clinician’s choice. It is designed for children over 6, and it detected more relevant allergens than the T.R.U.E. Test, which is FDA-approved only for ages 6–17. The ACDS Core and NACDG series test MI at a higher, more reliable concentration (Tam & Yu 2022). The series was published in the ACDS journal Dermatitis, and the AAD’s journal JAAD carries the main review of how to use it (Neale 2021 Part 2). No commercial patch panel has an FDA indication for children under 6. For toddlers, experts build custom panels based on what the child is exposed to and test the family’s own products. A 2–4-year-old’s back holds about 40–45 allergens, standard concentrations and contact times are generally used, and a repeat open application test (ROAT) of a suspect product on the forearm is a useful extra step. Treatment is avoiding the allergen. The ACDS CAMP database can produce a list of products free of the child’s allergens. The Pre-Emptive Avoidance Strategy suggests that avoiding the top 10 personal-care allergens could prevent about a third of paediatric ACD (Tam & Yu 2022). The evidence here is moderate: registries and expert consensus, with no randomised trials.

Patch Testing [defines] Allergic Contact Dermatitis American Academy of Dermatology [relates] Patch Testing Dupilumab [relates] Patch Testing

What parents report (evidence: anecdotal). In an r/eczema thread about a toddler with severe AD on Dupilumab, other parents mostly suggested allergy work-up and swapping to fragrance-free soaps and detergents. One parent said “Dreft has a really strong fragrance” and moved to a free-and-clear detergent, “every little thing can help”. The same thread shows the confusion around testing: parents are told to “see an allergist”, but blood or prick tests for IgE Food Allergy do not detect contact allergy. Only patch testing does.

Food Allergy [relates] Allergic Contact Dermatitis

Connections

• Chamomile — reported from chamomile tea and Kamillosan cream, source: DermNet
• Calendula — marigold contact sensitisation ~2%, source: Reider 2001
• Atopic Dermatitis — 36.9% of AD children patch-positive vs 26.4% without AD, source: Bonamonte 2022
• Patch Testing — the only diagnostic test; Pediatric Baseline Series for >6 y, source: Tam & Yu 2022; Neale 2021
• Fragrance Allergy — top paediatric allergen group, source: Tam & Yu 2022
• Methylisothiazolinone — 3.7% of patch-tested Italian children, source: Bonamonte 2022
• Lanolin — 1.2–6.2% of patch-tested children; more common in AD, source: Tam & Yu 2022
• Neomycin — long-standing top paediatric allergen, source: Tam & Yu 2022
• Essential Oils — linalool/limonene hydroperoxides, tea tree and lavender ACD, source: DermNet 2020; Barbaud 2023
• Compositae Allergy — parthenolide more often positive in AD children, source: Tam & Yu 2022
• Topical Corticosteroids — tixocortol pivalate (steroid allergy marker) more often positive in AD, source: Tam & Yu 2022
• Emollient Therapy — emollient ingredients (lanolin, CAPB, propylene glycol) are common culprits, source: Tam & Yu 2022
• No Moisture Therapy — product-specific ACD is a reason to change emollient, not stop all, source: No Moisture Therapy note
• Shea Butter — first shea contact-allergy case 2024, source: Castelain 2024
• Petrolatum — essentially no contact-allergy risk; lanolin substitute, source: Cutis 2023
• Differential Diagnosis of Toddler Eczema — localised mimic/overlap; patch testing, source: Türe Avcı 2026