The toddler with the runny nose that never quite clears, eczema that flares overnight, or a cough that turns up at 2am every winter — household allergens are usually somewhere in the picture. None of this is exotic. House dust mites, the cat, damp behind the bath panel: ordinary stuff that, when targeted properly, often makes the difference. For a wider view, see our complete guide to child health.
House Dust Mite
Dust mites are microscopic relatives of spiders, around 0.3 mm long, that live in mattresses, pillows, sofas, soft toys and carpets. They eat shed human skin. The allergen isn't the mite — it's a protein called Der p 1 in their droppings, and it's everywhere a mite has lived.
In atopic toddlers (eczema, asthma, allergic rhinitis), dust mite allergy is one of the most common environmental triggers. The pattern is recognisable: eczema that's worse in the morning after a night in bed, a blocked or runny nose that won't shift, sneezing on waking, itchy red eyes, and a night cough or wheeze that's particularly noticeable in autumn and winter when the heating goes on and windows stay shut.
What actually moves the needle:
- Wash bedding weekly at 60°C. Below 55°C the mite survives — a 40°C wash leaves them alive and well. If a duvet won't take 60°C, tumble drying on hot for an hour after washing kills mites by desiccation.
- Allergen-proof encasings on the mattress, pillow, and duvet. The tightly woven fabric (pore size under 10 microns) is the single change with the best evidence in trials when used consistently.
- Replace bedroom carpet with hard flooring if you can. If you can't, vacuum twice weekly with a HEPA-filtered cleaner — the filter matters because ordinary vacuums redistribute fine allergen back into the air.
- Soft toys: keep one or two, not twenty. The keepers go in the freezer for 24 hours every couple of weeks, then through a 60°C wash.
- Humidity below 50%. Dust mites can't drink — they pull water from the air and die when relative humidity stays under about 45–50%. A £10 hygrometer tells you where you are; a dehumidifier or just consistent ventilation gets you there.
- Cut the dust traps. Open shelves of books, fabric storage boxes, and heavy curtains in a child's bedroom all hold reservoirs of allergen. Glass-fronted bookcases and washable blinds are easier.
Pet Dander — Mostly Cats
Cat is the bigger problem here. The allergen is Fel d 1, produced in the cat's saliva and sebaceous glands, deposited on fur during grooming, and carried into the air on tiny particles that stay airborne for hours and stick to walls, clothes, and school bags. Fel d 1 has been measured in classrooms where no cat has ever been — children carry it in on jumpers. This is also why a child with a strong cat allergy can react in a flat where a cat lived six months ago.
Dog dander (Can f 1) is similar in mechanism but generally less potent.
If a toddler is reacting to your cat:
- The cat doesn't sleep in the bedroom. Ever. This is the most useful single change short of rehoming.
- HEPA-filtered vacuum on hard floors and soft furnishings, twice weekly.
- Wash the cat weekly if it tolerates it — reduces airborne Fel d 1 modestly for a few days.
- Keep the child's hands washed after stroking, and out of the eyes in the meantime.
- Air the bedroom daily; consider a HEPA air purifier sized for the room volume if symptoms are persistent.
Rehoming the cat produces the largest improvement, but Fel d 1 takes 4–6 months to clear from the house even after the animal has gone — so the change isn't instant. Many families decide they can live with partial measures; that's a legitimate choice once you've named it openly.
Mould
Mould spores grow wherever there's chronic damp: behind a leaking shower seal, around a cold-spot in a corner of an external wall, on window frames where condensation pools, in a kitchen with no extractor fan. The spores become airborne and trigger eczema, rhinitis and asthma in sensitised children — symptoms tend to be worse in late summer and autumn when outdoor counts are also high.
The treatment is the damp, not the child:
- Run extractor fans during and for 15 minutes after every shower or bath.
- Open windows after cooking; lid pans where you can.
- Fix leaks promptly — a slow leak under a bath produces an enormous reservoir of allergen behind the panel.
- Wipe down window frames where condensation collects.
- Visible mould patches under about a square metre can be cleaned with a fungicidal wash; have the child elsewhere while you do it. Anything larger, or recurrent after cleaning, needs the building cause addressed.
- A dehumidifier in a persistently damp room is more useful than air freshener.
If your toddler is in damp social housing and the landlord isn't acting, the GP can write to support a complaint — the legal threshold for action tightened materially in England after Awaab Ishak's death in 2020.
Cockroach (Less Common, Worth Knowing)
In the UK, cockroach allergen is mainly a problem in older blocks of flats with shared waste systems. The allergen Bla g 2 is in droppings and shed body parts and is a recognised trigger for asthma and rhinitis. If you see them, environmental health and the landlord both need to know — domestic sprays don't solve an infestation that's coming from elsewhere in the building.
Working Out Whether It's Allergy
Before any blood tests, a two-week diary is the single most useful tool. For each day note: where the child slept, whether you went anywhere different, what the weather was like, and what the symptoms were. Patterns you're looking for:
- Worse on waking, better through the day → think dust mite.
- Worse at granny's house with the cat, better at home → cat dander.
- Worse in autumn or in a particular room → mould.
- Always there, no clear pattern, food-related → less likely environmental, more likely something else.
Take this to your GP. Skin prick testing or specific IgE blood testing (still sometimes called RAST) is available — the GP can refer for it. Be aware that a positive test means the child has produced IgE antibodies; it doesn't on its own prove the child reacts clinically. About 8% of the general population is sensitised to cat without symptoms. The test result has to be read alongside the diary and the examination.
When to Refer to a Specialist
Reasonable thresholds for a paediatric allergist or respiratory paediatrician:
- Eczema that isn't controlled on a good regimen of emollients plus appropriate-strength topical steroid.
- Recurrent night cough or wheeze, or a confirmed or strongly suspected asthma diagnosis.
- More than one suspected environmental allergen and the picture isn't clear.
- You're thinking about subcutaneous or sublingual immunotherapy — generally offered from age 5 and considered when symptoms are persistent despite standard measures.
The honest framing for parents: you don't have to rehome the cat next Tuesday. You do have to decide what changes you're willing to make, give them eight weeks, and see what happens. Most toddlers improve substantially with a tight bedroom strategy and one or two of the bigger steps — and that result tells you what's actually driving the symptoms more clearly than any test.
Key Takeaways
The big four indoor allergens are house dust mite (specifically the protein Der p 1 in their droppings), cat dander (Fel d 1), mould spores, and — in some homes — cockroach. Most of the gain comes from a handful of changes: bedding washed at 60°C weekly, allergen-proof encasings on mattress and pillow, indoor humidity kept under 50% with a hygrometer, and the cat banned from the bedroom. Skin prick or specific IgE testing tells you about sensitisation, not whether a child reacts in real life — that's a clinical judgement. Refer to paediatric allergy when eczema isn't holding on standard treatment, when night cough/wheeze keeps recurring, or when you're considering immunotherapy (offered from age 5).
