Childhood asthma: what the evidence says on diagnosis and inhaled steroids

Childhood asthma is best diagnosed with an objective test of the airways rather than symptoms alone, and once it is confirmed, a daily inhaled corticosteroid is the treatment that controls it [s1]. That drug's benefit is well established, and so is its main drawback in children — a small reduction in growth that is largest in the first year of treatment and does not simply accumulate year on year [s2][s3]. Understanding both halves is what separates good asthma care from either under-treatment or needless worry.

Getting the diagnosis right first

The most consequential change in recent guidance is at the very start. The joint British Thoracic Society, NICE and SIGN guideline published on 27 November 2024 sets out how to diagnose, monitor and manage asthma in adults, young people and children, and it presses for objective testing rather than a label pinned on wheeze and a hunch [s1]. It lays out different diagnostic routes for children aged 5 to 16 and for children under 5, in whom objective tests are harder and a period of watchful treatment and review is often needed [s1].

This matters because asthma is both over- and under-diagnosed in children. A wheeze in a toddler with a cold is common and frequently outgrown; true asthma is a longer-running pattern of reversible airway narrowing. Fixing an accurate diagnosis is what makes the rest of the plan — the right drug, at the right dose, for the right child — defensible.

What inhaled corticosteroids actually do

Inhaled corticosteroids are recommended as first-line preventer therapy for children with persistent asthma [s3]. The clearest window on their effect in the youngest children comes from the PEAK trial, which randomised 285 children aged two or three at high risk of asthma to inhaled fluticasone at 88 micrograms twice daily or placebo for two years, followed by a year off all study medication [s2].

During the two treatment years the drug worked as intended: children on fluticasone had a greater proportion of symptom-free days (P=0.006) and a lower rate of flare-ups (P<0.001) than those on placebo [s2]. But in the third, treatment-free year, the groups were indistinguishable on symptom-free days, exacerbations and lung function — meaning the steroid controlled the disease while it was being taken but did not alter its underlying course once stopped [s2]. That is the honest frame for parents: this is control, not cure.

The growth question, in numbers

The most common worry about inhaled steroids in children is growth, and the evidence supports taking it seriously without overstating it. A Cochrane review pooled 25 randomised trials in 8,471 children with mild to moderate persistent asthma and found that, compared with placebo or non-steroidal drugs, inhaled corticosteroids reduced linear growth velocity by a mean of 0.48 cm per year over the first year of treatment (95% confidence interval 0.65 to 0.30 cm) [s3].

Crucially, the effect did not compound. In the second year of treatment there was no statistically significant difference in growth velocity between treated children and controls (mean difference 0.19 cm per year, 95% CI 0.48 lower to 0.11 higher, P=0.22) [s3]. The PEAK trial showed the same shape: children on fluticasone were 1.1 cm shorter than placebo children at 24 months (P<0.001), but the gap had narrowed to 0.7 cm by the end of the trial (P=0.008) [s2]. The picture is a one-off, front-loaded dip rather than a runaway loss — and it is weighed against fewer symptoms, fewer flare-ups and fewer courses of oral steroids, which carry their own risks.

Triggers and the rest of the plan

Beyond the preventer inhaler, management rests on identifying and reducing exposure to triggers, checking that a child can actually use their device, and reviewing control regularly rather than only when things go wrong [s1]. Common triggers include respiratory infections, allergens and air pollution; our coverage of the paediatric asthma burden from nitrogen dioxide sets out the outdoor-air side of that, and our review of air purifiers for allergy and asthma weighs the indoor one.

The role of the quick-relief (reliever) inhaler has also shifted in modern guidance, away from reaching for a short-acting reliever alone; we cover that change in detail in our explainer on what reliever inhalers do [s1].

How to read this without overreaching

The evidence supports a measured conclusion. Confirm the diagnosis objectively, treat persistent asthma with an inhaled corticosteroid because it demonstrably improves control, and monitor a child's growth as part of routine review rather than as a reason to withhold effective treatment [s1][s2][s3]. The growth effect is real, modest and largely limited to the first year; poorly controlled asthma and repeated courses of oral steroids are the larger threat to a child's wellbeing.

The limits are worth stating. PEAK studied preschoolers at high risk, not every child with asthma, and its follow-up ended at three years [s2]. The growth review graded its evidence as moderate quality and could not fully resolve differences between individual steroid molecules and devices [s3]. And the 2024 guideline is a framework for clinicians, not a script that fits every child [s1].

This article is informational and is not medical advice. It does not recommend any inhaler, dose or change to a child's treatment, and any concern about a child's asthma or medication should be discussed with a qualified clinician.