Dermex-S is a combination of two medicines: Clobetasol and Salicylic Acid, which treats eczema and psoriasis. Clobetasol is a steroid which blocks the production of certain chemical messengers (prostaglandins) that make the skin red, swollen and itchy. Salicylic Acid is a keratolytic medicine which breaks down keratin clumps, removes dead skin cells and softens the skin. It also enhances the absorption of Clobetasol into the skin.