Tar is a viscous liquid byproduct obtained from the manufacturing of organic products such as coal, wood, or peat, and tar ointment refers to an over-the-counter preparation of a topical solution that contains tar as its base. These topical solutions tend to be medicated soaps, creams, or shampoos. Tar ointment is frequently used as a treatment for conditions that cause flaky or scaly skin, but can also be used to kill head lice.
One of the most common forms of tar ointment is coal tar, which is still widely used to treat skin conditions such as psoriasis, dermatitis and eczema. Although the use of tar products has somewhat declined as newer compounds and drugs are developed for these skin ailments, they still have the advantages of being cheap and causing less overall toxicity than many modern therapies. For example, although topical steroids can be very effective at treating psoriasis, they also can lead to thinning of the skin and pigmentation changes, and excessive use can cause them to be absorbed into the body and result in organ damage.
Skin diseases such as psoriasis tend to cause an increase in the life cycle of skin cells, leading to the buildup of dead cells on the surface of the epidermis. This results in thick, itchy, and dry patches of skin. It is not known exactly how coal tar ointments treat skin conditions like psoriasis, but it is thought that they mainly work as keratolytic agents, or agents that inhibit excessive cell growth, which leads to loosening and softening of the dry skin patches. Coal tar ointment also appears to have antimicrobial properties, leading to less risk of skin infections. Additionally, it reduces itching.
Few side effects are associated with tar ointment other than slight skin irritation, but it can be very messy to apply, may stain clothes, hair, or skin, and often has a strong odor. For these reasons, most people prefer to use this ointment at night. Newer and refined forms of tar ointment have been developed that tend to be less irritating to the skin and less likely to cause staining, but these refined forms are also slightly less effective than the crude forms.
Tar ointment may cause sun sensitivity, so patients are advised to avoid prolonged sun exposure and wear sunscreen or protective clothing while outside. In certain cases, patients who do not respond to this treatment may receive a combined therapy of tar ointment and ultraviolet B (UVB) phototherapy, which involves exposing a patient to an artificial UVB light source for a specified period of time. These combined therapies should only be performed under a doctor’s supervision to prevent overexposure to UVB light and possible skin damage.