In the nineties, tar came under close FDA scrutiny due to its various side effects, including carcinogenesis. Other potential problems include irritancy, odor, staining and photosensitization. When using a tar formulation, read the label closely. Tar formulations should never be used on cats because felines are incredibly sensitive. Adverse effects of tar may include hair loss or, in extreme cases, death.
Selenium offers anti-bacterial, keratolytic and drying functions.
Some experts recommend Selsun Blue to treat Malassezia infections. It also offers follicular flushing, which is important because hair follicles can become infected with bacteria such as Staphylococcus intermedius. Finally, it is useful in treating hot spots and pyotraumatic dermatitis. Benzoyl peroxide should be used with topical ectoparasiticides as it may wash them off. Hot spots usually are secondary to a predisposing factor such as a flea bite or an inhalant allergy that causes obsessive scratching, biting, licking or chewing.