Hahnemann prepared Causticum by decomposing potassium hydrate with freshly slaked lime, distilling the caustic watery fraction (“tinctura acris sine kali”) which, though not a simple chemical entity, acts consistently as a caustic, alkaline, proteolytic medium. Crude properties produce corrosive irritation of mucosae, warty excrescences, and trophic weakness of nerves and muscles. In homoeopathy, triturations and potencies from the distilled liquor are used. The remedy’s neuro-trophic stamp—pareses, contracting tendons, vocal cord paralysis, ptosis, facial palsy, together with rawness of mucosae, warty growths, and a strong justice/compassionate mental colouring—maps back to this peculiar alkaline distillate. [Hahnemann], [Hughes], [Allen], [Clarke]

Hahnemann’s proving (Chronic Diseases) revealed burning rawness, hoarseness → aphonia, facial and limb weakness, contracted tendons, urinary incontinence/retention with paralytic bladder, warts, chaps and fissures, and a deep emotional axis: fear for others, weeping from sympathy, inability to tolerate injustice. Confirmations abound in post-diphtheritic paralysis, Bell’s palsy, ptosis, writer’s cramp, torticollis, spasmodic dysphonia, stress/ exposure-induced aphonia, post-viral neuropathies, warts (especially on hands/face, pedunculated or flat), burn-like pains with rawness, and urinary dysfunction. [Hahnemann], [Hering], [Allen], [Clarke], [Kent], [Boger], [Boericke], [Farrington], [Phatak], [Tyler], [Nash]