Tar

Preparations:

  • Precipitated (most commonly used in Dermatology)
  • Sublimed
  • Colloidal
  • Sulfurated potash
  • Sulfurated lime
  • Washed sulfur

Mechanism of action unclear

  • Antiproliferative effects: suppression of DNA synthesis, synergic with UV radiation  
  • Anti-inflammatory: Decrease neutrophil chemotaxis (shale tar only)
  • Antifungal: mechanism of action not known (shale tar only)

1) Coal tar:

  • Psoriasis; atopic dermatitis; seborrheic dermatitis; Tinea versicolor; dermatophyte / yeast infections; vitiligo; pruritus

2) Wood tar:

  • Psoriasis

3) Shale tar:

  • Psoriasis; seborrheic dermatitis; dermatophyte / yeast infections

* For further reading refer to a pharmacology source

Carcinogenesis:

  • Keratinocyte carcinoma & scrotal SCC historically (major carcinogenic agents: benzapyrene, anthracene and pyridines) 
  • Aesthetic: smell, appearance, stain clothes
  • Phototoxicity (UVA): Coal tar mainly (phototoxic compounds: anthracene, acridine, fluoranthene, benzapyrene, phenanthrene)
  • allergic contact dermatitis (especially photoallergy): Wood tar (cross-reaction with colophony, balsam, turpentine)
  • Other: irritant contact dermatitis & acneiform eruptions, pruritus, folliculitis, comedones, keratoses (tar warts), and keratoacanthomas

Tar derived from 3 sources:

1) Crude coal tar: 

Most commonly used in dermatology; contains polyaromatic hydrocarbons, phenols & nitrogen; most carcinogenic & phototoxic;

LCD (liquor carbonis detergens): alcohol extract of coal tar emulsified with polysorbate; more cosmetically acceptable but inferior therapeutically

2) Wood tar:

Less carcinogenic (only polyaromatic hydrocarbons); more irritant contact dermatitis (high phenols) & photoallergy 

3) Shale / Bituminous tar:

Derives from marine fossil; least carcinogenic; anti-inflammatory properties