Dust Almanac

Western red cedar

Thuja plicata · Cupressaceae · softwood

Also known as: red cedar, WRC, giant arborvitae, Pacific red cedar, British Columbia cedar

Region: Pacific Northwest, North America

Planed board of western red cedar with streaky salmon-pink to reddish-brown heartwood and straight, tight grain.

Western red cedar is a light, aromatic, rot-resistant softwood from the Pacific Northwest. It is widely used for shingles, siding, decking, fencing, outdoor furniture, sauna panelling, and boats.

Health hazards

  • Cancer

    Evidence: Applies to all wood dust

    IARC classifies all wood dust as carcinogenic to humans, mainly linked to cancer of the nasal cavity and sinuses after long-term heavy exposure. This applies to every species, so dust control matters whatever you cut.1

    Effects
    nasal and sinus cancer
    Exposure route
    inhalation
    From
    dust

  • Asthma / respiratory allergy

    Evidence: Confirmed in clinical testing

    Western red cedar is one of the best-documented causes of wood-dust asthma, confirmed by inhalation challenge in hundreds of British Columbia workers and linked to plicatic acid. Many people kept having asthma after they stopped working with it, and ACGIH flags it as a respiratory sensitizer.23456

    Effects
    occupational asthma, rhinitis
    Exposure route
    inhalation
    From
    dust

  • Skin allergy

    Evidence: Confirmed in clinical testing

    Patch testing confirmed allergic contact dermatitis from western red cedar sauna panelling in three Finnish cases, and ACGIH flags it as a skin sensitizer. The UK HSE also lists dermatitis.756

    Effects
    allergic contact dermatitis
    Exposure route
    skin
    From
    dust, heartwood

  • Respiratory irritation

    Evidence: Listed by an agency

    The UK HSE lists irritation of the nose, throat, and eyes (mucous membranes) for western red cedar dust.6

    Effects
    mucous membrane irritation
    Exposure route
    inhalation
    From
    dust

  • Whole-body (systemic) effects

    Evidence: Listed by an agency

    The UK HSE lists central nervous system effects for western red cedar without further detail. We did not find a primary report describing this.6

    Effects
    central nervous system effects
    Exposure route
    inhalation

Not finding a hazard listed here does not mean this wood is safe. All wood dust is hazardous; see how to protect yourself.

Exposure limits

Workplace exposure limits (8-hour average, mg/m³)
BodyLimitNotes
ACGIH TLV0.5 mg/m³ (inhalable)8-hour time-weighted average, as restated by OSHA source
UK WEL (softwood)5 mg/m³Applies to all softwood dust
NIOSH REL1 mg/m³Recommended limit for all wood dust

Compare limits across agencies.

Cancer classifications

Known compounds

  • plicatic acid: main cause of red cedar asthma source

Eastern white cedar (Thuja occidentalis) contains plicatic acid too and cross-reacts with western red cedar (Cartier-1986). Spanish cedar (Cedrela) and aromatic red cedar (Juniperus virginiana) are different trees.

Sources

  1. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Wood Dust and Formaldehyde. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 62. Lyon: International Agency for Research on Cancer; 1995. Link
  2. Chan-Yeung M, Barton GM, MacLean L, Grzybowski S. Occupational asthma and rhinitis due to Western red cedar (Thuja plicata). Am Rev Respir Dis. 1973;108(5):1094-102. Link
  3. Chan-Yeung M, Lam S, Koener S. Clinical features and natural history of occupational asthma due to western red cedar (Thuja plicata). Am J Med. 1982;72(3):411-5. Link
  4. Chan-Yeung M, MacLean L, Paggiaro PL. Follow-up study of 232 patients with occupational asthma caused by western red cedar (Thuja plicata). J Allergy Clin Immunol. 1987;79(5):792-6. Link
  5. US Occupational Safety and Health Administration. Occupational Chemical Database: Wood Dust. Last updated 06/23/2023. Link
  6. Health and Safety Executive. Toxic woods. Woodworking Information Sheet No 30 (Revision 1), WIS30(rev1). HSE; first published 11/2012. Withdrawn from hse.gov.uk (404 since c. Jan 2020); archived copy cited. Link
  7. Huilaja L, Kubin ME, Riekki R. Contact allergy to finished woods in furniture and furnishings: a small allergic contact dermatitis epidemic to western red cedar in sauna interior decoration. J Eur Acad Dermatol Venereol. 2016;30(1):57-9. Link
  8. Cartier A, Chan H, Malo JL, Pineau L, Tse KS, Chan-Yeung M. Occupational asthma caused by eastern white cedar (Thuja occidentalis) with demonstration that plicatic acid is present in this wood dust and is the causal agent. J Allergy Clin Immunol. 1986;77(4):639-45. Link

Last reviewed .