The lips, gums, tongue and buccal membranes are often invaded by generalized dermatoses, such as the exanthemata, angioneurotic edema, urticaria, herpes zoster, herpes simplex, pompholyx, dermatitis herpetiformis, pemphigus, psoriasis, erythema multiforme, leukemia, xanthoma, adenoma sebaceum, lichen planus, lupus erythematosus, lupus vulgaris, syphilis, lepra and precancerous keratoses. Actinomycosis and blasto-mycosis are rarely found in this cavity. Epithelioma, on the other hand, is exceedingly common on the lips and only a little less frequent on the remainder of the mucous tract of the mouth.
There are a number of fairly distinct affections of the tongue, lips and contiguous mucous membranes which are seen often enough in dermatologic practice to warrant brief description. For the most part, they seem unrelated to real dermatoses. The principal conditions of this variety are known as perleche, Fordyce’s disease, cheilitis, furrowed tongue, black tongue, transitory plaques of the tongue and leukoplakia.