Coal Tar (Monograph)

Drug class: Keratoplastic Agents
ATC class: D05AA
CAS number: 8007-45-2

Medically reviewed by Drugs.com on Feb 19, 2025. Written by ASHP.

Introduction

Coal tar has keratoplastic and mild local irritant properties.

Uses for Coal Tar

Coal tar preparations are used topically alone or in combination with other drugs (e.g., salicylic acid, sulfur) for controlling dandruff, seborrheic dermatitis, or psoriasis. Although there are few well-controlled studies demonstrating their efficacy, coal tar preparations are used and generally considered effective for relieving the itching and scalp flaking associated with dandruff; for relieving the itching, irritation, and skin flaking associated with seborrheic dermatitis; and for relieving the itching, redness, and scaling associated with psoriasis. However, patient acceptance of coal tar is very poor because it is extremely messy, malodorous, and stains skin and hair, and coal tar preparations have largely been replaced for many of these uses by other agents (e.g., topical antifungal agents, topical corticosteroids). Although coal tar has been further modified or refined to potentially provide more esthetically acceptable and pharmaceutically practical preparation, there currently are no published data showing that these modified or refined preparations of coal tar are superior to or even equal in clinical efficacy to coal tar.

Coal tar and coal tar preparations have been used in the past under the supervision of a clinician in conjunction with ultraviolet (UV) or sunlight for controlling psoriasis (i.e., Goeckerman therapy^{† [off-label]}). More recently, however, coal tar preparations have been replaced first by anthralin and then by lubricating bases in the Goeckerman regimen.

Coal tar and coal tar preparations also have been used topically in the management of other dermatologic disorders (e.g., eczema^{† [off-label]}, atopic dermatitis^{† [off-label]}, chronic exudative or lichenoid dermatitis^{† [off-label]}).

Coal Tar Dosage and Administration

Administration

Coal tar preparations are applied topically to the scalp as a shampoo or to the skin as a bath, cake, cream, gel, lotion, ointment, or solution. Coal tar preparations are for external use only and contact with the eyes should be avoided. (See Cautions: Precautions and Contraindications.) Coal tar preparations should not be applied in or near the anogenital area unless otherwise directed by a physician. (See Cautions: Carcinogenicity.)

Dosage

Dosage of various coal tar preparations is not well established since well defined standards for specific contents of these preparations currently do not exist. (See Chemistry and Stability: Chemistry.)

For relief of itching and scalp flaking associated with dandruff; itching, irritation, and skin flaking associated with seborrheic dermatitis of the scalp; or itching, redness, and scaling associated with psoriasis of the scalp, coal tar preparations intended for use as a shampoo should be applied to wet hair and massaged vigorously into the scalp. Then, the scalp is rinsed thoroughly and application of the lotion and rinsing is repeated. Coal tar preparations intended for use as a shampoo usually are used twice weekly.

When coal tar preparations are used as a bath for relief of signs and symptoms associated with psoriasis or seborrheic dermatitis of the body or other dermatologic conditions of the body, an appropriate amount of these preparations should be diluted in lukewarm bath water. The coal tar preparation should be thoroughly mixed throughout the bath water. The patient should immerse himself into the bath and soak for 10–20 minutes. Bathing with a coal tar preparation may be performed once daily to once every 3 days; the usual duration of therapy is 30–45 days. If the physician prescribes the Goeckerman treatment (coal tar and phototherapy) for psoriasis, all of the coal tar preparation should be removed from the skin prior to exposure to radiation. Phototherapy may begin 2–72 hours after bathing with the coal tar preparation. A determination of the minimum phototoxic dose (MPD) of UVB, UVA, or UVA/B radiation should be made by the physician for each patient; the initial dosage of radiation should be suberythemal and should not exceed the MPD. The usual cautions associated with Goeckerman therapy should be followed. (See Cautions: Precautions and Contraindications.)

When coal tar preparations are applied directly to the skin for relief of signs and symptoms of psoriasis or seborrheic dermatitis of the body or other dermatologic conditions of the body, the coal tar preparation usually is applied topically to the affected area 1–4 times daily. When a coal tar preparation is applied once daily, it may be preferable to apply the preparation at bedtime. Coal tar preparations should be gently massaged into the area of application. After several minutes, any excess amount of the preparation should be removed with tissues. Removing excess amounts of the preparation may minimize staining of the skin and clothing. Once the condition has been controlled, it may be possible to decrease the frequency of application to 2 or 3 times weekly. If dryness of the skin occurs during use of the gel, an emollient may be applied to the treated area 1 hour after application of the coal tar gel or coal tar extract gel. If the physician prescribes the Goeckerman treatment for psoriasis, the coal tar preparation is applied once or twice daily at bedtime and/or at least 30–60 minutes prior to UV radiation. All of the coal tar preparation should be removed from the skin prior to radiation. The dosage of UV radiation must be individualized for each patient by the physician. The usual cautions associated with Goekerman therapy should be followed. (See Cautions: Precautions and Contraindications.)

Cautions for Coal Tar

Adverse Effects

Coal tar preparations may produce dermatitis, sometimes severe, when used for prolonged periods. Dermatitis may be allergic or irritant in nature. Irritant effects increase with increasing concentration. Topical application of coal tar preparations in hypersensitive patients may elicit a pustular eruption or keratocystic response. Prolonged use of strong coal tar preparations may produce a painless, chronic folliculitis (tar acne). Coal tar-induced folliculitis generally clears following discontinuance of the preparation or a reduction in frequency of application, and may be avoided by leaving the treated area exposed, by not applying the preparation on hairy areas, and by not using the preparation for extended periods. Coal tar preparations are malodorous, frequently stain the skin and hair (especially in patients with blonde, bleached, dyed, or gray hair), and may not be well accepted by the patient. Coal tar preparations also may stain clothing. Coal tar preparations produce photosensitivity reactions, and exposure of treated areas to sunlight or sunlamps (UVA and/or UVB light) should be avoided. (See Cautions: Precautions and Contraindications.)

Adverse reactions to coal tar preparations reportedly occur more frequently with coal tar than with other coal tar preparations (i.e., extracts, fractionates, distillates, and spirits).

Precautions and Contraindications

Coal tar preCoal tar and coal tar preparations have been used in the past under the supervision of a physician in conjunction with ultraviolet (UV) or sunlight for controlling psoriasis (i.e., Goeckerman therapy^{† [off-label]}). In subsequent years, however, coal tar preparations have been replaced first by anthralin and then by lubricating bases in the Goeckerman regimen.

Coal tar and coal tar preparations also have been used topically in the management of other dermatologic disorders (e.g., eczema^†, atopic dermatitis^†, chronic exudative or lichenoid dermatitis.^†)

Preparations are intended for external use only. Coal tar preparations should not be used near the eyes; if contact with the eye(s) occurs, the affected eye(s) should be rinsed thoroughly with water. If coal tar preparations are used for self-medication and the condition worsens or persists after regular use as directed, the preparation should be discontinued and a clinician should be consulted. Patients should be advised to discontinue use of the preparation and to consult a clinician if skin irritation develops or increases during coal tar therapy.

Patients should be advised to avoid exposure to direct sunlight or sunlamps (UVA and/or UVB light), unless otherwise directed by a clinician (e.g., during the Goeckerman treatment for psoriasis), for at least 24 hours (one manufacturer recommends 72 hours) after application of coal tar preparations since a photosensitivity reaction may occur. Prior to exposure to sunlight, coal tar preparations should be completely removed from the skin unless otherwise directed by a clinician. Because of the risk of photosensitivity reactions, coal tar preparations should generally not be used to treat disorders such as lupus erythematosus, polymorphous light eruptions, or other conditions that are characterized by photosensitivity. When the Goeckerman treatment for psoriasis is used, care must be taken to prevent overexposure of the treated areas to UV light and/or sunlight during therapeutic UV radiation or following such treatment since serious burns may result. Patients undergoing the Goeckerman treatment for psoriasis should use sunscreening or sunblocking agents or protective clothing for at least 24 hours after treatment to protect the treated areas against additional UV exposure from sunlight. In patients undergoing this treatment, care should be taken to avoid application of coal tar preparations and/or subsequent sunlight exposure over normal skin since new psoriatic lesions may appear in the areas of trauma (Koebner phenomenon).

Coal tar preparations should not be applied to acutely inflamed or broken skin or to infected lesions unless otherwise directed by a clinician. Coal tar preparations generally should not be used in patients with an exacerbation of psoriasis since total body exfoliation may be precipitated. Coal tar preparations are contraindicated in patients with a history of hypersensitivity to these preparations and specific preparations are contraindicated in patients with a history of hypersensitivity to any ingredient in the formulation.

Pediatric Precautions

Safety and efficacy of coal tar preparations in children have not been established.

Carcinogenicity

Coal tar has been shown to be carcinogenic in humans following topical exposure. Chronic exposure to concentrated solutions of topical coal tar in industrial settings has been associated with skin cancer; however, the average period of exposure in these individuals was 20–24 years. The carcinogenic potential of coal tar was first described in chimney sweeps; scrotal cancer in chimney sweeps who started working at an early age and continued working through puberty was attributed to the soot and coal tar that lodged in their clothing. In a review of the literature for the possible occurrence of cancer in patients treated with coal tar, only 13 cases of skin cancer attributable to coal tar were reported during the period of 1900–1966; 2 of these patients also had been treated with arsenic. Most of these patients developed skin cancer in the anogenital region. Therefore, coal tar preparations should generally not be applied topically in the anogenital region. Data reported and included in the Third National Cancer Survey on patients using coal tar indicate that the incidence of skin cancer in patients treated with coal tar ointment is not increased compared with the expected incidence of skin cancer for the general population. It has been suggested that psoriasis may selectively protect against skin cancer.

It is generally accepted that coal tar contains carcinogenic substances. Biochemical studies indicate that coal tars used medically contain different carcinogens but in uneven concentrations. Carcinogens contained in coal tar are produced in the coking oven during the heating of coal because of the release of cancer-causing organic free radicals. The higher the temperature (1000°C and greater) in the coking oven, the greater and more varied is the production of free radicals. The smaller free radicals combine to produce polynuclear hydrocarbons, which are generally considered as the principal carcinogens in coal tar. At least 75 polynuclear hydrocarbons have been identified in coal tar. A number of animal studies have confirmed the carcinogenic potential of coal tar.

Although most experts recognize the concern regarding the carcinogenic potential of topically applied coal tar preparations, they generally believe that the contact time of a shampoo is of such short duration that this concern should not prevent the use of coal tar preparations on the scalp. However, the risk of cancer cannot be dismissed when coal tar preparations are used in the treatment of seborrheic dermatitis of the body and psoriasis, since the coal tar preparation is intended to remain in contact with the skin for prolonged periods and to be used chronically in these conditions. Although available information does not indicate an increased incidence of skin cancer in psoriatic patients treated with coal tar preparations, additional study is needed to determine the risk. The carcinogenic potential of combined therapy with coal tar preparations and UV radiation has not been fully determined. Although one study reportedly found an increased risk of skin cancer in patients with high exposure to coal tar preparations and UV radiation compared with those lacking high exposure, another study reportedly found that the incidence of skin cancer in patients receiving combined therapy with coal tar preparations and UV radiation was not appreciably increased compared with the expected incidence of skin cancer for the general population.

Pregnancy and Lactation

Pregnancy

Animal reproduction studies have not been performed with coal tar preparations. It is not known whether coal tar preparations can cause fetal harm when used topically by pregnant women. Coal tar preparations should be used during pregnancy only when clearly needed.

Lactation

It is not known whether topically applied coal tar is absorbed and/or distributed into milk. Because of the potential for serious adverse reactions (i.e., carcinogenicity) from coal tar preparations in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

Drug Interactions

Although no known drug interactions have been reported to date, it is recommended that coal tar preparations not be used concomitantly with drugs (e.g., tetracyclines, psoralens, tretinoin) having phototoxic and/or photoactivating potential.

Pharmacology

Coal tar has keratoplastic and mild local irritant properties. When used in the management of dandruff, seborrheic dermatitis, or psoriasis, coal tar preparations reduce the number and size of epidermal cells produced. The precise mechanism by which coal tar exerts this therapeutic action is not known. It has been suggested that coal tar abstracts oxygen from the skin, thereby inhibiting cell reproduction (mitosis) and causing a decrease in the size and number of cells in the stratum germinativum and stratum corneum. It also has been suggested that coal tars formulated in various soaps and shampoos exert their therapeutic action in patients with dandruff, seborrheic dermatitis, or psoriasis by penetrating the epidermis and removing the scales produced by these skin disorders. Some of the polyphenolic substances and peroxides in coal tar may react with epidermal sulfhydryl groups to produce an effect on skin that is similar to that resulting from exposure to sunlight; this effect could theoretically decrease epidermal proliferation and dermal infiltration.

In addition to decreasing the size and number of epidermal cells produced in various skin disorders, coal tar reportedly has vasoconstrictive, astringent, weak antiseptic, and antipruritic properties. Coal tar also has a photosensitizing action.

Chemistry and Stability

Chemistry

Coal Tar (Crude Coal Tar)

Coal tar (crude coal tar, pix carbonis) is the tar obtained as a by-product during the destructive distillation of bituminous coal. Coal tar is produced during the coking of coal for the steel and gas industries. Coal tar occurs as a nearly black, viscous liquid that is heavier than water and has a characteristic, naphthalene-like odor, is faintly alkaline, and produces a sharp, burning sensation on the tongue. Coal tar is slightly soluble in water, to which it imparts its characteristic odor and taste and a faintly alkaline reaction; partially soluble in acetone, in alcohol, in carbon disulfide, in chloroform, in ether, in methanol, and in solvent hexane; more soluble in benzene, with only about 5% remaining undissolved; and almost completely soluble in nitrobenzene, with only a small amount of undissolved matter remaining suspended in the solution.

Coal tar is a mixture of tar acids and hydrocarbons that polymerize at high temperatures to reportedly form some 10,000 different compounds. When coal tar is subjected to fractional distillation, the first fractions obtained are complex mixtures referred to as light oils, middle or carbolic oils, heavy or creosote oils, and anthracene oils; pitch, a nonvolatile residue, remains in the still. The composition varies substantially and is complex, but generally, coal tar consists of 2–8% light oils (mainly benzene, toluene, xylene), 8–10% middle oils (mainly phenols, cresols, and naphthalene), 8–10% heavy oils (naphthalene and derivatives), 16–20% anthracene oils (mostly anthracene), and about 50% pitch. The physical and chemical composition of coal tar varies according to the geographic source of the coal and the conditions of carbonization, including the temperature, type, and efficiency of the coke oven used in its preparation, and according to various other factors. Low-temperature coal tar is distilled at 450–700°C and generally contains 20% or more middle oils, and high-temperature (gas-house) coal tar is distilled at 900–1200°C and generally contains middle oils in concentrations not exceeding 8–10%; however, the composition of these tars also is variable. When distilled in a vertical retort, low-temperature coal tar contains high concentrations of tar acids (e.g., phenol, cresols) and low concentrations of naphthalenes. High-temperature coal tar contains relatively low concentrations of tar acids but a medium to high proportion of naphthalenes when distilled in a horizontal retort, and contains high concentrations of tar acids but a low proportion of naphthalenes when distilled in a vertical retort. Most coal tar available in the US is supposedly high-temperature coal tar.

Official (e.g., USP, BP) compendial monographs on coal tar do not specify the composition of the tar, other than to require that not more than 2% of 100 mg of coal tar remain as a residue (ash) on ignition. Since coal tar is not a chemical entity and its therapeutic effect depends on a myriad of carbonized and volatile constituents, it is unlikely that achievement of complete and absolute uniformity of clinical results can occur; however, development of better, official compendial standards, including a chromatographic tar profile and other adequate chemical and physical specifications, will better ensure that coal tar contains minimal rather than substantial variations in composition. Because of the lack of specifications for coal tar, a Joint Industry Coal Tar Project is attempting to develop a standard of quality that potentially will lead to an effective, uniform coal tar product with the smallest quantity of undesirable components.

Coal tar also has been obtained from anthracite coal; anthracite coal contains more carbon and less hydrogen than bituminous coal.

Other Coal Tar Preparations

Coal tar often is further modified or refined into coal tar extract, coal tar topical solution, and coal tar distillate. Only coal tar (crude coal tar), coal tar topical solution, and coal tar ointment are official USP preparations. When coal tar, which is of complex and unknown composition, is refined by various methods to potentially obtain more esthetically acceptable and pharmaceutically practical products, the pharmacologically active components in the final product may be altered qualitatively and quantitatively. Although differences in therapeutic activity have not been shown when coal tars from various sources have been used, some experts believe that the degree of refinement of coal tar is responsible for variation in therapeutic effectiveness of different coal tar products.

Coal Tar Topical Solution

Coal tar topical solution (liquor carbonis detergens, liquor picis carbonis) is prepared by mixing 200 g of coal tar with 500 g of washed sand and then adding 50 g of polysorbate (Tween) 80 and 700 mL of alcohol and macerating the mixture for 7 days in a closed vessel with frequent agitation; the mixture is then filtered, and the vessel and filter rinsed with sufficient alcohol to make the final product measure 1 liter. Polysorbate 80 is used in the preparation of coal tar solution as an emulsifying agent. When coal tar topical solution is mixed with water, a fine dispersion of coal tar results, aided by the presence of polysorbate 80. Although each 100 mL of coal tar topical solution represents 20 g of coal tar, and commercially available preparations are labeled as containing 20% coal tar, coal tar topical solution doesnotcontain 20% coal tar since an undetermined amount of insoluble components of the tar are filtered out of the suspension during preparation of the solution. The labeled amount of coal tar in coal tar topical solution represents the amount of coal tar initially added to the washed sand, polysorbate 80, and alcohol, and not the amount of coal tar remaining in the extract after filtration. In one study, about 7% tar fractions were present in coal tar topical solution after extraction.

Coal Tar Extract

Coal tar extract is similar to coal tar topical solution except that other solvents are used to extract the various components from coal tar. Coal tar extract is not an official preparation and standards for its composition do not exist. Various methods for extracting coal tar are used during the manufacture of commercially available products labeled as containing coal tar extract. Polyoxyethylene lauryl ether, 2-ethylhexyloxystearate, polyethylene glycol 40 sorbitan peroleate, and other substances have been used in the preparation of coal tar extract. Although equivalencies of coal tar extract to coal tar have been estimated by some manufacturers, standards for such determinations do not currently exist.

Coal Tar Distillate

Coal tar distillate is obtained by distilling tar with an aromatic hydrocarbon solvent and consists of all the volatile products of the tar freed from the pitch. Coal tar distillate occurs as a dark, brownish-red, fairly mobile liquid with a penetrating odor. Coal tar distillate is not an official preparation and standards for its composition do not exist.

Coal Tar Ointment

Coal tar ointment (unguentum picis carbonis) is prepared by blending 10 g of coal tar with 5 g of polysorbate (Tween) 80 and then incorporating the mixture with 985 g of zinc oxide paste. Coal tar ointment (unofficial) also has been prepared using washed coal tar. Washed coal tar is prepared by stirring or agitating coal tar with about 5 times its volume of purified water and then pouring off the separated water; the washing process may be repeated several times and then the remaining coal tar is dried by heating on a hot water bath.

Stability

Coal tar preparations should be stored in tight or well-closed containers and protected from freezing. The viscosity of coal tar gradually increases on exposure to air. Coal tar burns in air with a luminous, sooty flame. Because of the variety of commercially available coal tar preparations, the manufacturer’s recommendations should be followed with respect to specific storage requirements.

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

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