Pets and Eczema

Pets come up in two different questions about toddler eczema. The first is whether living with a dog or cat in early life changes the chance of a child developing Atopic Dermatitis. The second is whether pet dander and saliva trigger flares in a child who already has eczema. The NHS lists pets among things that can make atopic eczema worse. Allergy UK says “there is no evidence that animals cause eczema”, but that animal saliva and fur can irritate or worsen it, and advises keeping pets off the bed and sofa. All the evidence on the first question is observational, from birth cohorts. No trials of pet removal for eczema were found.

Pets and Eczema [part-of] Environmental Triggers Pets and Eczema [relates] Atopic Dermatitis

Dogs: a fairly consistent protective association. A meta-analysis of 21 birth cohorts (Pelucchi et al., J Allergy Clin Immunol 2013) found that exposure to dogs was linked with a lower risk of atopic dermatitis (RR 0.72, 95% CI 0.61–0.85; 15 studies). For pets overall the RR was 0.75 (0.67–0.85). Medscape cites a study in which having a dog at home at birth was associated with about a 50% lower incidence of AD at age 3. In the US CCAAPS cohort of 636 infants of atopic parents, living with a dog in the first year was protective up to age 4 (OR 0.4, 95% CI 0.2–0.7). Children sensitised to dog who had not lived with a dog had nearly four times the risk of eczema (aOR 3.9, 1.6–9.2). Children sensitised to dog who had lived with one were not at increased risk (Epstein et al., J Pediatr 2011). A proposed explanation is the Hygiene Hypothesis: dogs bring bacteria into homes that may shape the infant immune system or the Skin Microbiome (Ownby & Johnson 2011).

Hygiene Hypothesis [relates] Pets and Eczema Pets and Eczema [prevents] Atopic Dermatitis Skin Microbiome [relates] Pets and Eczema

Cats: null overall, possibly harmful in some children. In the same meta-analysis, cat exposure showed no association with AD (RR 0.94, 0.76–1.16; 13 studies). Within CCAAPS, children who lived with a cat in their first year and became sensitised to cat had a much higher risk of eczema at age 4 (aOR 13.3, 3.1–57.9). In two European cohorts, cat exposure raised eczema risk only in children with a Filaggrin loss-of-function mutation (HR 11.1 in Copenhagen; 3.82 in Manchester). This was evident from 2 months of age, before IgE sensitisation usually develops. Dog exposure was protective only in Copenhagen (HR 0.49) (Bisgaard 2008, cited in Ownby & Johnson 2011). An earlier systematic review (Langan et al. 2007) pooled protection from both cats (OR 0.79) and dogs (OR 0.68). However, the one cohort that adjusted for families with allergies avoiding pets found no effect, and that review concluded there was “no convincing evidence” of protection.

Filaggrin [relates] Pets and Eczema Pets and Eczema [triggers] Atopic Dermatitis

Conflict: [Pelucchi et al., J Allergy Clin Immunol, 2013] says early-life dog exposure is protective (RR 0.72) and cat exposure has no association. [Epstein et al., J Pediatr, 2011] says cat ownership combined with cat sensitisation raises eczema risk 13-fold, and [Bisgaard et al., PLoS Med, 2008, via Ownby & Johnson 2011] says neonatal cat exposure raises risk in filaggrin-mutation carriers. [Langan et al., Arch Dermatol, 2007, via Ownby & Johnson 2011] says there is no convincing protective effect once pet-avoidance behaviour is accounted for. Unresolved — add to open_questions.

Avoidance for a child who already has eczema. No RCT of pet removal for eczema was found. NICE CG57 places pets among the inhalant allergens to consider when a child has seasonal flares, eczema with Asthma or Allergic Rhinitis, or facial eczema at age 3 or over. Skin Prick Testing or specific IgE can show sensitisation, but sensitisation alone does not prove that the pet drives the eczema. The National Eczema Society suggests keeping pets out of bedrooms, putting a washable blanket on the pet’s favourite chair, brushing pets regularly (their coats carry Pollen) and using a high-filtration vacuum. It warns that pet allergen takes up to 8 weeks to fall in a home, “so short-term rehoming of pets is not worth trying”. Ownby & Johnson (2011) note that over 90% of US homes have measurable cat and dog allergen whether or not a pet has lived there. Medscape suggests that for children with animal allergy, parents consider removing animals or keeping them out of the child’s areas.

Skin Prick Testing [relates] Pets and Eczema NICE CG57 [relates] Pets and Eczema

What parents report (evidence: anecdotal). In r/eczema, a parent of a 9-month-old whose blood test showed cat allergy kept the cat. They added an air purifier and an antihistamine with the paediatrician’s approval, and reported that eye-rubbing fell after replacing an overdue home air filter. Other commenters called keeping the cat “really selfish”, which shows how emotive the topic is. Another parent observed that “the older my daughter got, the better her eczema got, even around animals”. In r/toddlers, families with mild dog or cat sensitisation kept their pets and focused on skin care; one started sweeping and mopping daily because “we have dogs, which I think is a trigger”. In an older thread, a paediatrician “kind of implied” rehoming a cat for a 2-month-old; the family chose to try controlling the eczema first.

Connections

• Environmental Triggers — pet dander and saliva as flare triggers, source: NHS; Allergy UK
• Atopic Dermatitis — dog RR 0.72, cat RR 0.94 (birth cohorts), source: Pelucchi 2013
• Filaggrin — cat exposure plus FLG mutation raises risk, source: Bisgaard 2008 via Ownby 2011
• Hygiene Hypothesis — microbial exposure from dogs as explanation, source: Ownby & Johnson 2011
• Skin Microbiome — pets alter home bacterial communities, source: Ownby & Johnson 2011
• Skin Prick Testing — sensitisation ≠ clinical trigger, source: Epstein 2011
• NICE CG57 — inhalant allergy criteria, source: NICE CG57 1.4.1.3
• Pollen — carried on pet coats, source: National Eczema Society
• Allergic Rhinitis — pets mainly trigger airway allergy, source: Allergy UK