Eczema that starts after childhood is a large minority of adult cases, not a curiosity: roughly one adult in four with atopic dermatitis dates it to adulthood, and British cohort data put the figure higher still. What changes in an adult is not the genome, which was fixed at birth. It is the exposure: what the hands touch, how often the skin is wetted and stripped, and, in women, where in a hormonal cycle the barrier is sitting.
How much adult eczema starts in adulthood
Lee and colleagues pooled observational studies reporting age of onset beyond ten years. Twenty-five met the inclusion criteria and 17 reported onset after age 16 with enough data to pool. The pooled proportion of adult-onset disease was 26.1% (95% confidence interval 16.5 to 37.2%). Heterogeneity was extreme at I² = 99.3%, so the interval is the honest number to carry away, not the point estimate (Lee et al, 2019).
British birth cohort data sit at the top of that interval. Abuabara and colleagues followed the 1958 National Child Development Study and the 1970 British Cohort Study into midlife. Of those with eczema, 40% in the 1970 cohort and 43% in the 1958 cohort reported the disease for the first time in adulthood. Period prevalence ran at 7% to 14% during any given period in childhood and 5% to 12% during any given period in adulthood (Abuabara et al, 2019). Adult eczema is largely not childhood eczema carried forward. The childhood-onset side of that split begins earlier than most people assume, often within the first twelve months, and it is assessed against a different guideline and a different evidence base.
The adult presentation is not the childhood one
Across those same studies, adult-onset cases showed higher rates of foot dermatitis and of personal history of atopy, and lower rates of flexural lesions (Lee et al, 2019). The inner elbow and back of knee pattern that defines eczema in a child is a weak guide in an adult, which is one reason adult-onset disease is often called something else first. Facial involvement has its own pattern and its own irritants (eczema on the face), and the overlap with contact and seborrhoeic dermatitis is where the misclassification tends to happen.
Wet work is the exposure adults acquire
Visser and colleagues genotyped Dutch apprentice nurses and followed 446 of them through one to three years of traineeship, recording exposure and symptoms on diary cards. One hundred and thirty subjects, 29%, reported hand eczema on one or more occasions during their traineeships. Frequent hand washing during traineeships, more than 8 times per shift, and frequent hand washing at home, more than 10 times per day, increased the risk, with odds ratios of 2.2 and 1.8 (Visser et al, 2014).
The mechanism is mechanical rather than allergic. Palm skin has no sebaceous glands and the backs of the hands very few, so lipid removed by a surfactant is not replaced at the rate it is lost, and each wash starts from a slightly worse baseline than the last. Healthcare, catering, cleaning, hairdressing and childcare all raise the daily count without anyone counting it.
The measurement is the action. Count the actual washes in one shift rather than estimating them, then cut what can be cut: cotton liners inside rubber gloves for wet work, emollient at every sink rather than one tube by the bed, rings off before anything wet. The irritant and allergic breakdown is in hand eczema.
Why the barrier gives way now and not before
In the same nurse cohort, FLG mutations were present in 11.1% of subjects. On their own, in people with no history of atopic dermatitis, they showed no effect on hand eczema risk (odds ratio 0.7). Combined with a history of atopic dermatitis, the odds ratio was 3.6 (Visser et al, 2014).
That pairing is the useful part. Filaggrin bundles keratin so the outer cells flatten into a tight layer, then breaks down into the small molecules that hold water in the surface and keep it acidic. A loss-of-function variant is present from birth and does not switch on at 30. It sets how much daily insult the skin absorbs before it fails, so a genotype that was survivable through an office job stops being survivable through a ward rota (the skin barrier).
Hormonal windows in women
Prevalence separates by sex after puberty, at 6.04% in men and 8.01% in women across European and United States figures. Oestrogen and progesterone mostly enhance Th2 and regulatory T cell activity while suppressing Th1 and Th17, and the epidermal permeability barrier is impaired by androgens and progesterone but restored by oestradiol (Kanda et al, 2019). Two hormonal effects therefore run in the same direction during the luteal phase: a barrier that repairs more slowly and an immune bias tilted towards the atopic side. The NHS lists hormonal changes, such as during pregnancy, among the triggers that worsen atopic eczema. Cycle, pregnancy and perimenopausal patterns, and what to do in each window, are in eczema and hormones.
Working out which change did it
Adult onset has a before and an after, which childhood onset does not, and that is the diagnostic advantage. The NHS also names stress among the triggers that worsen atopic eczema, and the pathway runs through nerve endings and mast cells rather than through any allergen, so a flare can arrive with nothing new in the house (stress and eczema).
Work backwards over the twelve months before the first patch: job, home, water, products, pets, medication, workload. Then test the candidates rather than ranking them by suspicion. A daily tracking log covering products and exposures alongside severity separates real patterns from remembered ones, and a structured dietary trial does the same for food. For a suspected contact allergy, patch testing is the specialist test. Dermatology departments use it to find out whether a skin condition is caused, or made worse, by an allergy to something that has touched the skin, typically across three appointments in one week, screening the 50 or so commonest culprits: metals, perfumes, rubber chemicals, preservatives, cosmetics and plants (British Association of Dermatologists, Patch testing).
References
- Lee HH, Patel KR, Singam V, Rastogi S, Silverberg JI. A systematic review and meta-analysis of the prevalence and phenotype of adult-onset atopic dermatitis. Journal of the American Academy of Dermatology, 2019. https://doi.org/10.1016/j.jaad.2018.05.1241
- Abuabara K, Ye M, McCulloch CE, et al. Clinical onset of atopic eczema: results from 2 nationally representative British birth cohorts followed through midlife. Journal of Allergy and Clinical Immunology, 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6721832/
- Visser MJ, Verberk MM, Campbell LE, McLean WHI, et al. Filaggrin loss-of-function mutations and atopic dermatitis as risk factors for hand eczema in apprentice nurses: part II of a prospective cohort study. Contact Dermatitis, 2014, 70:139-150. https://pmc.ncbi.nlm.nih.gov/articles/PMC4357292/
- Kanda N, Hoashi T, Saeki H. The roles of sex hormones in the course of atopic dermatitis. International Journal of Molecular Sciences, 2019, 20:4660. https://pmc.ncbi.nlm.nih.gov/articles/PMC6802354/
- NHS. Atopic eczema. https://www.nhs.uk/conditions/atopic-eczema/
- British Association of Dermatologists. Patch testing. https://www.skinhealthinfo.org.uk/condition/patch-testing/