Coal tar

Coal tar is a thick, dark, viscous by-product of the incomplete combustion of coal. It is a complex mixture of thousands of compounds, including polycyclic aromatic hydrocarbons (PAHs), phenols, and aromatic amines. Coal tar has been used for centuries in dermatology, particularly in the treatment of chronic skin conditions such as psoriasis, seborrheic dermatitis, eczema, and dandruff, due to its keratoplastic, anti-inflammatory, antipruritic, and antifungal properties.

Although considered a traditional therapy, coal tar remains in use today due to its effectiveness, especially when combined with phototherapy or corticosteroids. However, concerns regarding its potential carcinogenicity and unpleasant odor have led to the development of refined preparations with lower toxicity and better cosmetic acceptability.

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1. Classification and Source

• Pharmacologic class: Keratoplastic agent

• Therapeutic class: Dermatologic agent

• Natural origin: By-product of coal carbonization

• ATC code: D05AA (Antipsoriatics, coal tar-based)

• Forms used in medicine:

  • Crude coal tar

  • Refined coal tar

  • Liquor carbonis detergens (LCD): a solution of coal tar in alcohol and surfactant

  • Coal tar solution (USP)

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2. Chemical Composition

Coal tar contains over 10,000 individual constituents, including:

• Polycyclic aromatic hydrocarbons (PAHs) – e.g., anthracene, phenanthrene

• Phenol derivatives

• Cresols

• Xylenes

• Benzene derivatives

The medicinal value is primarily attributed to PAHs, which interact with the skin to modulate keratinocyte function and inflammatory response.

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3. Mechanism of Action

The precise mechanisms are not fully elucidated, but coal tar acts through several pathways:

• Keratoplastic effect: Normalizes keratinocyte proliferation and differentiation; slows epidermal turnover

• Anti-inflammatory action: Reduces neutrophil infiltration, cytokine production, and oxidative stress

• Antipruritic effect: Possibly related to local anesthetic properties and modulation of itch pathways

• Antifungal activity: Especially effective against Malassezia species in seborrheic dermatitis

• Photosensitizing effect: Enhances ultraviolet light responsiveness (used in Goeckerman therapy)

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4. Therapeutic Indications

A. FDA-Approved and Widely Accepted Uses

• Psoriasis vulgaris (plaque-type, scalp, palmoplantar)

• Seborrheic dermatitis (scalp and facial)

• Eczema (chronic)

• Dandruff

• Lichen simplex chronicus

B. Off-label and Traditional Uses

• Atopic dermatitis (rare due to irritation)

• Tinea versicolor (antifungal adjunct)

• Ichthyosis

• Pityriasis rosea

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5. Formulations and Products

Coal tar is available in multiple forms and concentrations, typically ranging from 0.5% to 20%, depending on the formulation.

A. Topical Forms

Form	Typical Uses
Creams/ointments	Chronic plaque psoriasis, eczema
Gels and lotions	Scalp psoriasis, seborrheic dermatitis
Shampoos	Dandruff, seborrheic dermatitis
Soaps	General skin maintenance in chronic dermatitis
Bath additives	Whole-body management in psoriasis
LCD (liquor carbonis detergens)	Prescription topical applications

B. Commercial Brand Examples

• Polytar® (shampoo)

• Neutrogena T/Gel® (shampoo)

• Exorex® (lotion)

• Balnetar® (bath additive)

• Psoriasin® (gel)

• LCD preparations (often compounded)

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6. Dosage and Administration

• Apply 1–4 times daily, depending on severity and tolerance

• For shampoos, use 2–3 times per week:

  • Massage into scalp

  • Leave for 5–10 minutes

  • Rinse thoroughly

• Bath additives: Dilute as directed, soak for 10–15 minutes

• Avoid mucous membranes and broken skin

Duration of use depends on clinical response. Chronic use should be monitored for side effects.

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7. Efficacy

Coal tar is generally less effective than potent topical corticosteroids but is useful in maintenance therapy, especially in combination with:

• Phototherapy (Goeckerman regimen): Coal tar + UVB light, highly effective in severe psoriasis

• Topical corticosteroids: Tar can reduce tachyphylaxis, steroid-sparing

• Salicylic acid: Enhances penetration and effectiveness

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8. Advantages

• Inexpensive

• Long history of use

• Effective for chronic scaling conditions

• Useful in steroid-sensitive areas for long-term use

• Can be used in pediatric populations with supervision

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9. Adverse Effects

A. Local Irritation

• Itching

• Stinging

• Erythema

• Contact dermatitis (due to allergens like phenols, PAHs)

B. Photosensitivity

• Increased risk of sunburn

• Avoid UV exposure immediately after application

C. Folliculitis

• Especially in occluded areas or with prolonged use

D. Cosmetic Concerns

• Stains clothing and bed linen

• Unpleasant tar-like odor

• Skin discoloration (yellow-brown)

E. Allergic Reactions

• Rare, but possible; patch test if needed

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10. Carcinogenicity Concerns

• Occupational exposure to crude coal tar (chimney sweeps, road workers) is linked to skin and scrotal cancers

• Medicinal coal tar is refined and used at low concentrations

• Regulatory agencies (EMA, FDA) acknowledge minimal cancer risk from short-term, topical use

Long-term use should be monitored, especially in Goeckerman therapy, though studies show low incidence of malignancy in dermatologic use.

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11. Contraindications

• Hypersensitivity to coal tar or any excipients

• Broken or infected skin (increased absorption and irritation)

• Photodermatoses

• History of skin cancer or precancerous lesions

• Pregnancy and lactation: use only if necessary; limited systemic absorption

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12. Precautions

• Use with caution on face, genitalia, and intertriginous areas

• Avoid occlusive dressings unless directed

• Avoid concurrent use with photosensitizing agents

• Warn patients about staining of clothes, hair, and skin

• Caution in pediatric use: monitor for irritation

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13. Drug Interactions

Coal tar is topical with minimal systemic absorption, so systemic drug interactions are rare. However, avoid:

• Concurrent UV therapy without supervision (risk of burns)

• Topical retinoids or corticosteroids in the same area simultaneously without clinician direction

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14. Monitoring and Follow-Up

• Assess for irritation, sensitization, or contact dermatitis

• Monitor long-term users for:

  • Signs of skin thickening

  • Atypical pigmentation

  • Any new skin growths

• Review treatment efficacy every 2–4 weeks

• Counsel patients on application technique and expectations

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15. Special Populations

A. Children

• Use low concentrations with supervision

• Short-term use only; higher risk of irritation and folliculitis

B. Pregnancy

• Category C (USA): No controlled data; avoid unless necessary

• Topical use likely safe at low concentrations

C. Elderly

• Skin may be thinner and more sensitive

• Caution in intertriginous and atrophic areas

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16. Regulatory and Safety Considerations

• OTC status in many countries for low-concentration shampoos and creams

• Prescription required for higher concentrations or compounded LCD

• FDA Monograph for OTC Drug Use: Coal tar concentrations between 0.5–5% for psoriasis, dandruff, and seborrheic dermatitis are GRASE (Generally Recognized As Safe and Effective)

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17. Alternatives

A. Pharmacologic

• Topical corticosteroids

• Vitamin D analogs (e.g., calcipotriol)

• Calcineurin inhibitors (e.g., tacrolimus)

• Tazarotene

• Salicylic acid

B. Non-Pharmacologic

• Phototherapy (NB-UVB)

• Moisturizers and emollients

• Oatmeal baths

• Coal tar-free antifungal shampoos (for dandruff)