People assume they are allergic to dust – more likely is that they are allergic to dust mites (HDM).  These are microscopic, and tend to reside in fabrics in the home esp bedding, carpets, sofas.  So your house can be spotless but still be full of mites!

There are a number of different house dust mite species – most are Dermatophagoides (“skin eating”…), D. farinae is the American type, D. pteronyssinus is the European one.

HDM allergy is common in atopic individuals, contributing to eczema, rhinoconjunctivitis and asthma. Eczema usually comes first, but sensitisation (usually develops in young children) seems to predict development of asthma persisting into school age!

Although common, it doesn’t tend to cause immediate reactions, the way cat/dog does, probably because mites don’t fly – so exposure only caused when surfaces disturbed or if skin/nose/mouth/eyes in direct contact. But inflammation may be chronic, from brief, low quantity, frequent exposure. So even with avoidance/ reduction measures, it can take months to see the benefit…

There is cross-sensitivity with shellfish allergy but not fish allergy.

In some parts of the world, mouse and cockroach allergies more of an issue.

Lots of different allergens identified.  der p 1 and 2 are major allergens in mite faeces, in kids with eczema various other allergens found in mite bodies also important. Mite faeces are the most important cause of sensitisation. Composition of skin prick solutions seems to vary…

Avoidance/reduction

Allergy UK has an advice leaflet with different measures for reducing levels of HDM in the home.  Evidence however is that this is difficult to do and rarely seems to have any significant clinical effect!  So no point in doing piecemeal, certainly.

Dust mites need high humidity to get water, so high altitude and air conditioning suppresses them.  They also like temperatures over 20deg. They are photophobic so hide deep in fabrics.

Get rid of carpets, curtains, excess cushions/pillow/throws, move soft toys off bed.

Wash bedding at 60, or tumble dry! Soft toys go in the freezer overnight once a month (in a bag, obviously, to avoid collecting smells). Protective covers for mattresses and hypoallergenic bedding materials.

Some vacuum cleaners are better than others (in theory) eg with HEPMA filter.  Allergy UK approves products (but only if company pay, of course). But the mechanical action of cleaning (plus moving furniture, changing beds etc) can whip particles up into the air (as can emptying the contents of the cleaner) so best done when kids are out, and wait 20 minutes before letting them back in…  Cleaning and replacing filters important too esp if bagless design.

Vacuuming alone resulted in a significant reduction in carpet house dust mite allergen concentration and load. Levels approached pretreatment values by 4 weeks posttreatment in the intensive vacuuming group, whereas combination of dry steam cleaning plus vacuuming lasted up to 8 weeks. 

You can also use a steam cleaner on a mattress!

Evidence for air purifiers is mixed.  If placed on carpet, they can actually disturb more allergen than they remove! You need to close doors and windows of course. Unfortunately the best ones tend to be big, expensive and noisy, and price does not mean good quality. Plus you have to remember to replace the filters. The cheapest Which? recommended one (the Electriq EAP500HC) costs over £200.

In PAXAMA study in the NW England (kids with a history of wheeze requiring a visit to hospital), impermeable covers (blinded!) halved risk of having an emergency hospital attendance over the next year. [Murray 2017] Maximum benefit was seen in under 11yrs, mono-sensitized to mite, living in nonsmoking households, and requiring more ICS.  

[JACI 2018]

Immunotherapy

Systematic review found good evidence of benefit for eczema with immunotherapy against house dust mite, with subcut immunotherapy superior to sublingual. [Journal of Allergy & Clinical Immunology. 151(1):147-158, 2023 PMID 36191689]

Evidence for immunotherapy for allergic rhinitis, at least in adults… Treatment effect from 14 weeks, so not rapid…

No evidence for asthma but given as indication… although research into whether HDM immunotherapy might prevent.

NICE approved Acarizax for moderate to severe HDM rhinitis from age 12 in the NHS in England in January 2025. Acarizax is sublingual therapy (derived from D pteronyssinus and D farinae), indicated in adolescents (12-17 years) as well as adults diagnosed by clinical history and a positive test of house dust mite sensitisation (skin prick test and/or specific IgE) with persistent moderate to severe house dust mite allergic rhinitis despite use of symptom-relieving medication.

NICE appraisal also comments that avoidance/reduction of HDM burden in home is almost impossible and if problems persist, it can induce strong feelings of guilt in parents/carers.

Also, many patients would prefer not to be using regular, large doses of steroids, even if effective.

£80 a month on NHS, has not been submitted to Scottish Medicines Consortium so currently not recommended.

International treatment guidelines refer to a treatment period of 3 years for allergy immunotherapy to achieve disease modification. Efficacy data is available for 18 months of treatment with ACARIZAX in adults; no data is available for 3 years of treatment. If no benefit in first year, no indication to continue.

First dose should be observed and the patient monitored for at least 30 minutes.

Place under the tongue, avoid swallowing for 1 minute, avoid food/drink for 5 minutes.

Contraindications are FEV₁ <70% of predicted value despite treatment, or severe asthma exacerbation within the last 3 months.

If oral ulceration, postpone treatment.

Eosinophilic oesophagitis has been reported.

See also Prevention, pregnancy, EAT/LEAP studies and immunotherapy.

One of the most common food allergies, and a frequent cause of anaphylaxis.  Peanut is technically a legume, although there is cross-reactivity with tree nuts so often included when people talk about “nuts”.  Always consider if there are potentially other allergies to lentils, sesame, tree nuts eg cashew etc.

Also known as groundnut or monkey nut.

[Gary Stiefel, Leicester Royal, BSACI guideline peanut allergy]

Diagnosis

Wide range of potential peanut proteins.  In US study, vast majority were Ara h1/2 positive, but European more diverse. h1, h2, h3 most common for systemic reactions.  You would think testing with whole peanut would be more sensitive but component testing probably more sensitive and specific than total IgE – but not better than skin prick testing.

With a decent history, SPT >3mm or IgE >0.35 sufficient.

Before proceeding to a hospital challenge, footnote suggests either 2 negatives, or else both IgE and SPT negative.

Distinguish Pollen Food Syndrome – ie older, rhinitis, oral allergy symptoms with nuts/fruit. These kids will have a milder allergy.  Hazelnut mostly (Cor a1) but almond, walnut too. But can coexist with more severe allergy! Doing grass/birch pollen would support diagnosis, doing components might help assess prognosis. If history unclear, but positive IgE/Skin prick test then do components h2 and h8 (list of different cut offs for different commercial products given, with related specificity/sensitivity, just says positive/negative in flow chart). Footnote suggests adding Ara h 1, 3 and 9 as also suggest primary peanut allergy even if Ara h 2 neg.

Sibling risk 5-9%. Too low to justify routinely screening.  If family likely to just avoid forever, living in fear, then consider SPT to encourage home challenge!?

Prognosis

Up to 20% will outgrow, usually before age 8. Review may not be necessary if PFS only.  Follow up is essentially about education.  Testing can be done periodically, depending on resources.

In a study of adults coming to allergy clinics, 10% of peanut allergic turned out not to be.  Partly this would have been because the diagnosis was wrong (many had never actually reacted to peanut in the past).  Having eczema meant you were more likely to still be positive on testing.  Having asthma and being male made it half as likely you would not be allergic anymore.  But many of the cases described were not formally challenged so these results are of limited value.  [Poster at AAI 2021, Rima Rachid]

Avoidance

Difficult, as often used in biscuits, chocolate, ethnic foods eg satay.

As for any food allergy:

• Safe food skills, that are then passed on to child, are essential.
• Allergy plan and teaching about anaphylaxis.

Peanut needs to be specified on food labels under UK/EU law.

Precautionary labels – impossible to eliminate risk. Often these “may contain” warnings and similar just say “nuts” without specifying whether the risk is from peanut or a tree nut (the company may be able to give further information if you enquire directly). 

Snack foods with precautionary labels are higher risk eg biscuits, cakes [Helen Brough].

Balance between convenience and risk (probably a very small risk, as many families ignore these warnings to some degree).  Stratify risk according to type of food, previous reactions, threshold, asthma, illness, time of day, location etc. Crossing the road metaphor – choose a safe place!

Should you avoid all nuts?  Some kids will be allergic to other (tree) nuts, but not all.  Andrew Clark reports v low rate of accidental reactions, 3%, with avoidance of all nuts. But increases quality of life to be allowed other nuts!  Risk assessment for each individual person!

Peanut oil

Probability of any reaction to refined peanut oil is remote (Blom et al, 2017). Little evidence that anyone has ever reacted to refined peanut oil. Code of practice is that presence of UNREFINED peanut oil should be declared on bottles of oil (UK and Europe).

But peanut oil, even if refined, still has to be declared on food labels.  Beware unrefined oil in ethnic foods.  Peanut oil also found in some medicines eg vitamins, antibiotic creams.

Some suspicion that peanut oil in cosmetics and pharmaceuticals might lead to sensitization and subsequent peanut allergy, even if not enough peanut protein to cause a reaction in an allergic person. So advice is avoid if you have a strong family history of allergy.

Immunotherapy

See Peanut immunotherapy.