Review
Topical tar: Back to the future

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The use of medicinal tar for dermatologic disorders dates back to the ancient times. Although coal tar is utilized more frequently in modern dermatology, wood tars have also been widely employed. Tar is used mainly in the treatment of chronic stable plaque psoriasis, scalp psoriasis, atopic dermatitis, and seborrheic dermatitis, either alone or in combination therapy with other medications, phototherapy, or both. Many modifications have been made to tar preparations to increase their acceptability, as some dislike its odor, messy application, and staining of clothing. One should consider a tried and true treatment with tar that has led to clearing of lesions and prolonged remission times. Occupational studies have demonstrated the carcinogenicity of tar; however, epidemiologic studies do not confirm similar outcomes when used topically. This article will review the pharmacology, formulations, efficacy, and adverse effects of crude coal tar and other tars in the treatment of selected dermatologic conditions.

Section snippets

Pharmacology of tar

Crude coal tar is one of 3 main types of tar, the others being wood tar (principally pine, beech, birch, and juniper) and shale (bituminous tars/ichthammols).10 Wood and shale tars lack contact sensitizing potential and/or photosensitizing effects, both qualities that coal tar possesses. Coal tar is heavier than water and is slightly soluble in it, resulting in a mildly alkaline solution. It also has a naphthalene-like odor with a sharp, burning taste.11 Coal tar is first made by heating coal

Adverse effects

Tar folliculitis is common side effect of coal tar, particularly because a chlorine-containing ingredient of tar is a follicular irritant. It usually occurs on the lower extremities with tar concentrations greater than 2%.2 In addition, acneiform eruptions have been noted with the use of tar, differing from acne vulgaris because the main inducer in this case is chloronaphthalene. It usually occurs in patches and is evident on the extensor surfaces of the arms, with pruritus as the main symptom.

The other tars

Wood tars, derived from the destructive distillation of pine, birch, beech, and juniper, contain acetic acid or phenolcarbonic acids, with a relative absence of toxic anthracene and pyridine derivatives.1, 45 Wood tars have been used in the treatment of various cutaneous disorders, including psoriasis and atopic dermatitis, and have no photosensitizing effects.3 An increased risk of irritation and allergic sensitization has been seen with their use.2, 10 In one study consisting of a population

Summary

Tar is a time-proven remedy for many skin disorders including psoriasis, atopic dermatitis, and seborrheic dermatitis. There are concerns regarding its carcinogenicity, with conflicting evidence in epidemiologic and human studies. Tar is still used in many countries as a first-line treatment because of cost savings and availability. It has a pharmacologic agent that has shown significant efficacy in psoriasis, atopic dermatitis, and seborrheic dermatitis. We consider it a key component in the

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    Funding sources: None.

    Conflicts of interest: None declared.

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