This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Arsenic is largely used by the profession, almost as a routine remedy, in cutaneous disease, but its value has been variously estimated by specialists of experience. We may exclude at once from its influence the ordinary acute exanthemata, also naevus, parasitic and syphilitic eruptions, and the rarer maladies of scleroderma, keloid, xanthelasma, and true leprosy. We may exclude also all forms of skin disease while in the acute stage, or while accompanied by marked inflammatory reaction, and then, speaking generally, we may say that as we have noted arsenic to be valuable in rheumatic, malarial, and neurotic affections, so is it also valuable in most cutaneous manifestations of these conditions. With regard to the last-mentioned, my own experience agrees rather with that of Hunt and of Anstie, as against Bazin and others, that in neurotic subjects with highly strung excitable natures, arsenic is less readily borne, and more usually causes diarrhoea.
The forms of skin disease in which the remedy is of generally accepted value, are such as psoriasis, eczema in the dry or scaling stage, pemphigus, lichen, alopecia, and chronic urticaria; and those in which its powers are more controverted are acne, lupus, ichthyosis, herpes zoster,1 sycosis, prurigo, epithelioma, cancer, and elephantiasis graecorum.