Topically applied creams and gels can be created with absorption enhancers.
Many chemicals need help to get through the protective skin barrier. Examples include ketoprofen (anti-inflammatory), lorazepam (anxiolytic, anti-nauseant), morphine (pain), cyclobenzaprine (muscle relaxant), lidocaine (topical anesthetic), ketamine (pain), and many others.
These links offer some information regarding some of the bases we frequently use.
PLO gel looks and feels like a cream but is actually a gel. Combining the aqueous phase (pluronic gel) with the lecithin oil base creates an emulsion that holds together due to the surfactant qualities of the pluronic gel and the viscosity of that gel at room temperature. Chilling a PLO will actually make it turn liquid and can allow the gel to separate back into its oil and aqueous phases (usually takes weeks for separation to occur).
DMSO can also be used for some applications.
Occasionally, DMSO and PLO are combined in the same product.
Liposomal creams are variations on what has been discussed above. Many compounding specialists (including us) have devised unique proprietary creams specifically designed for different absorption characteristics. This is an art that take years of knowledge and practice.