Definition: the vehicle into which active ingredients may be incorporated. Petrolatum (which may be stiffened with wax) is the most widely used greasy ointment base and is suitable for the incorporation of oleaginous materials. Lanolin-containing bases will absorb water (and dissolved materials) and form water-in-oil type emulsions. Water soluble (washable) bases are often derived from polymers of ethylene glycol (PEGS); these will absorb water and ingredients dissolved in the water. Ointment bases are usually pharmacologically inert but may entrap water and serve to keep the skin from dying or to provide an emollient protective film.