The external auditory canal provides an ideal environment for bacterial growth because it is warm and moist. Otic solutions and suspensions are used to treat infections in the external auditory canal. The solvents are typically glycerin, propylene glycol, vegetable oils (e.g., olive oil), mineral oils, or low molecular weight polyethylene glycols (e.g., PEG 300). These solvents adhere to the canal wall better than water or alcohol.
A formulation for ear wax impaction could contain carbamide peroxide, glycerin, hydrogen peroxide, and olive oil. The carbamide peroxide and hydrogen peroxide contribute a mechanical "bubbling" action that softens and breaks up dried cerumen. These two ingredients also have anti-infective properties.
Glycerin is hygroscopic and absorbs moisture which also helps soften cerumen. Olive oil is a softening agents and keeps the formulation in the ear longer because of its viscosity.
The itching associated with seborrhea, or psoriasis, can be treated with topical corticosteroid formulations. Otic gels and ointments are used in these formulations and they are applied directly to the skin of the ear. Otic ointments typically use petrolatum as the base.