Science
Mechanism of Action
Coal Tar modulates skin function by slowing the rapid growth of skin cells and acting as a keratolytic agent, softening keratin. Its mechanism involves correcting keratinocyte differentiation defects, crucial for conditions like psoriasis. It also exhibits antimicrobial, anti-inflammatory, and antipruritic properties, potentially via polycyclic aryl hydrocarbons such as carbazole. In atopic dermatitis, it activates the Aryl Hydrocarbon Receptor (AHR) signaling pathway, which enhances epidermal differentiation, increases filaggrin levels, and inhibits the IL-4/STAT6 pathway, leading to improved skin barrier function and dampened keratinocyte responses. Furthermore, it engages the AHR/NRF2 pathway to aid in detoxifying reactive oxygen species.
Research
Clinical Evidence
High confidenceN/A
Key findings
- 01 In a foam formulation, combined with clobetasol propionate 0.05% emollient foam, it effectively induced remission and maintained clearance for plaque psoriasis.
- 02 Crude coal tar incorporated into triamcinolone cream 0.1% applied twice daily is a common treatment for individual psoriasis lesions.
- 03 A leave-on solution containing 15% liquor carbonis distillate (equivalent to 2.3% coal tar) demonstrated significantly superior and more persistent improvement compared to prescription calcipotriol cream for moderate chronic plaque psoriasis.
- 04 A 5% liquor carbonis detergens solution resulted in a 48% improvement in psoriasis disease severity after 4 weeks of treatment.
- 05 This range is recommended for dandruff shampoo formulations to effectively treat and prevent itchy scalp and dandruff.
Transparency
Dusting Analysis
Coal Tar exhibits therapeutic effects as an OTC drug ingredient at concentrations between 0.5% and 5%. Formulations containing less than 0.5% are unlikely to provide the advertised benefits for conditions like dandruff, seborrhea, or psoriasis, potentially serving as a 'dusting' application without clinical efficacy.
The Formula
Formulation
Stability
A thick, nearly black, viscous liquid with a distinct odor, Coal Tar is stable across a wide pH range (3-10) and is heat tolerant. It exhibits partial solubility in organic solvents (e.g., acetone, ethanol) and can be dispersed in water, oil, cream/gel bases, and silicone.
Synergies
- Clobetasol propionate (0.05%) in foam formulations for plaque psoriasis
- Triamcinolone cream (0.1%) for localized psoriasis treatment
- UV radiation therapy for chronic plaque psoriasis
Conflicts
- Strong oxidizers
Safety
Safety Profile
The FDA monographs Coal Tar as a Category I (safe and effective) OTC drug ingredient for treating dandruff, seborrhea, and psoriasis at 0.5-5% concentrations. However, the Cosmetic Ingredient Review (CIR) Expert Panel deems data insufficient for safety assessment in cosmetic formulations (non-OTC drug). The Scientific Committee on Consumer Safety (SCCS) concluded that crude and refined coal tars, containing carcinogenic polycyclic hydrocarbons, are not safe for cosmetic products. It is classified as a known human carcinogen by the National Toxicology Program (NTP) and IARC. While occupational exposure is linked to various cancers, conclusive evidence regarding cancer risk from product amounts for psoriasis in humans is lacking. California mandates cancer warnings for OTC Coal Tar products exceeding 0.5%. Coal Tar is also a photosensitizer, inducing phototoxicity and increasing skin sensitivity to UV light for up to 24 hours post-application.
Your Skin
Skin Compatibility
Our Assessment
Verdict
While demonstrably effective for specific dermatological conditions at controlled concentrations as an OTC drug, Coal Tar carries significant safety concerns including its classification as a human carcinogen, making its inclusion in cosmetic formulations highly questionable and subject to stringent regulatory review.
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References
Sources