Formaldehyde-Induced Asthma

Formaldehyde induced asthma is occupational asthma attributed to formaldehyde exposure. Most cases arise from airway irritation, and true immunological sensitisation is uncommon. The attribution is debated and needs careful confirmation.

Exposure. Embalming, pathology and anatomy laboratories, dialysis and sterilisation units, resin and particleboard manufacture, textile finishing, foundry core making and hairdressing (keratin smoothing products).

Epidemiology. Irritant induced asthma follows high or accidental exposure. Chronic low level exposure is linked with airway hyperresponsiveness and rhinitis. Workplace limits are well under 1 ppm.

Other effects. Allergic contact dermatitis, eye and nose irritation, and nasopharyngeal cancer and myeloid leukaemia with high long term exposure.

Pathophysiology.

Formaldehyde is a water soluble irritant that injures upper and lower airway epithelium and stimulates sensory nerves, causing bronchoconstriction and neurogenic inflammation.

A minority develop specific IgE to formaldehyde bound to albumin. Persistent injury produces airway remodelling.

• Cough, wheeze, chest tightness and dyspnoea at work, with eye and nasal irritation, improving away from work.
• Burning throat and rhinitis.
• Delayed or night time symptoms in some.
• Hand and face dermatitis in handlers.

Red flags.

• Severe attacks needing urgent care.
• Persistent symptoms with fixed obstruction after a single high exposure.

• Work history including tasks, ventilation and measured exposure.
• Spirometry with reversibility of 12% and 200 mL, or methacholine challenge (PC20 under 8 mg/mL suggests asthma).
• Serial peak flow at least 4 times daily over at least 2 weeks at work and 2 weeks away.
• Specific inhalation challenge in a specialist centre, with attention to irritant effects at test concentrations. Specific IgE and skin tests are unreliable.
• Patch testing with formaldehyde when dermatitis coexists.

Differential diagnosis. Irritant induced asthma after a single exposure, work exacerbated asthma, hypersensitivity pneumonitis, vocal cord dysfunction, rhinitis, chronic obstructive pulmonary disease.

• Reduce exposure: closed systems, local exhaust ventilation, low emission products, substitution (for example alternatives to formalin in tissue fixation) and respirators as an adjunct. Move the worker when symptoms persist despite control.
• Budesonide with formoterol 200/6 micrograms inhaled, 1 inhalation twice daily as maintenance plus 1 inhalation as needed (adults and adolescents 12 and over). Usual maximum 8 inhalations in 24 hours, up to 12 for a short period. Monitor symptoms, spirometry, exacerbations and oral candidiasis; rinse mouth after use. No renal adjustment; step up or down by control.
• Exacerbation: salbutamol 100 microgram metered dose through a spacer, 4 to 10 puffs, repeated every 20 minutes for the first hour, then every 4 hours as needed. Maximum 10 puffs each dose. Monitor heart rate, potassium and oxygen saturation. Caution in arrhythmia and hyperthyroidism.
• Exacerbation: prednisolone 40 to 50 mg orally once daily for 5 days, with no taper. Maximum 50 mg daily. Monitor glucose and blood pressure. Caution in diabetes and peptic ulcer; acceptable in pregnancy when needed; no renal adjustment.

Monitoring. Review every 3 months initially with spirometry; workplace air monitoring.

Referral and escalation. Respiratory and occupational physician; workplace assessment; notification and compensation where a work cause is established.