The topical treatment of psoriasis includes various medications, some in use for a long time but still valid today, such as the keratolitics and reductors. The keratolytics – salicylic acid, urea, sodium chloride, magnesia usta, lactic acid, benzoic acid, retinoic acid etc.

diminish the cohesion of corneocytes thus facilitating the removal of scales and renewal of the horny layer. Besides its keratolytic effect, salicylic acid reduces hyperplasia in the proliferated skin. It is used alone or in association with other substances (urea, lactic acid, ichtammol, dithranol, corticosteroids etc.) under the form of ointments or solutions. Being absorbed percutaneously, toxic phenomena may occur when applied over large areas of skin or at over 10% concentration. Urea, with a less significant keratolytic effect than the salicylic acid and moisturizing action (ability to fix water) may be used alone or in association with other substances (sodium chloride, salicilyc acid, lactic acid etc.) in magistral or comercial preparation. The association urea–ClNa (urodium), licensed active principle, is indicated in psoriasis (Psorilys®, Xerolys®).

Reductors include tars, dithranol, butantron etc. Tars have a reductor action (vasoconstrictive), inhibit the function of mitochondria, suppress DNA synthesis in keratinocytes, and have antiinflammatory action. Thes come in many preparation containing coal tar, ichtammol (Xeryal P®, Mediket Ictamo® etc.), oleum cade etc. These preparation may cause skin irritation, rarely sensibbilisation, phototoxicity, folliculitis, their carcinogenic potential beeng under debate. Dithranol, a powerful reductor agent, cell proliferation inhibitor (reduces DNA synthesis and diminishes mitotic activity induces keratinocytic apoptosis) and immunomodulator, remains an effective and cheap mediaction devoid of systemic side effects. Short/term therapy (10–30 minutes) prevents the irritation of healthy skin. It is available as emulsion, cream, ointment, paste, stick, gel or patch. Can be associated with PUVAor oral retinoids, but not with topical corticosteroids (earlier relapses). Butantron is less irritating and similarly effective.