Many skin conditions are treated with topical medications. Instead of applying active medicine directly onto the skin, “vehicles” are combined with the chosen medication to aid in its delivery. Vehicles are inactive creams, lotions, solutions and/or ointments that change the properties of the medicine mixed into them – assisting its application.
The primary components of vehicles include powders, oils, and liquids. The inherent properties of these three ingredients is translated to the vehicle, and thus how the medicine is delivered on the skin. For example, a vehicle with a prominent liquid component can assist with the drying of wet skin lesions through evaporation, whereas oils can provide an occluding coating to the skin and enhance the penetration of the active medicine.
When vehicles are combined with active medicines, you get “formulations”. Formulations can be creams, ointments, lotions, solutions, and foams embedded with active medicine. Different formulations have different potencies (i.e. triamcinolone ointment is more potent than triamcinolone cream) and different body region applications (i.e. solutions for the scalp instead of creams). The consideration of which formulation to use is crucial, as certain formulations are easier to use, therefore promoting adherence to a treatment regimen and overall improvement of a patient’s skin condition.
Outline of formulations:
Creams are predominantly mixtures or emulsions of oils in water. Creams are usually white in color and easily rubbed in without leaving much of a residue. They are applicable to numerous body regions. For these reasons, they tend to be favored by patients and frequently prescribed by clinicians. Creams are particularly beneficial in the skin folds and offer a drying effect to help with wet or damp skin lesions. Additionally, certain creams can be “augmented”, meaning they are more potent and penetrate the skin deeper (i.e. betamethasone dipropionate vs. betamethasone dipropionate augmented). Because a cream is an oil in water emulsion, it requires added agents to keep the mixture stable. This is the same idea as the difference between oil and water salad dressings and a thicker one like ranch or thousand island.
Ointments are mainly composed of oils and greases with a small amount of water. Oils are translucent and greasy, with the latter characteristic making them cosmetically unfavorable for some patients. They provide great lubrication and can be used on dry skin lesions. Ointments are more occlusive, which allows for better penetration of medication through the skin and higher potency. Because of this effect, ointments may not always be indicated for certain regions of the skin that are naturally thinner than others (i.e. the face, armpits, groin folds, etc.). Ointments work best in smooth skin regions lacking hair and on thick and dry skin lesions.
Lotions are composed of powder and water. Lotions are easily spread but only slightly occlusive, making them the least potent topical vehicle. However, lotions are useful in the treatment of moist or exudative skin lesions, as they provide a drying effect through evaporation after application. Lotions can be useful in hairy areas of the skin, as well as large areas due to their ease of application.
Gels may appear similar to ointments, except they are composed of water, carboxymethylcellulose beads, propylene glycol, and occasionally alcohol. Gels are translucent, greaseless, and easy to apply. For comparison, think of the common surgical lubricant or K-Y Jelly. Gels dry and form a thin film, which does not stain or leave behind greasy texture. These features make gels cosmetically favorable, but they are poorly occlusive and do not provide hydration. Gels are particularly applicable for acne and hair-bearing areas, since they do not mat down the hair after drying.
Foams are composed of liquid film and gas bubbles. Foams easily spread and absorb into the skin while leaving behind little residue. Because of this, they are cosmetically appealing and more expensive formulations. Foams provide little to no hydration or occlusion. However, certain types of foams called emollient foams can provide skin hydration and build up the skin barrier - making them advantageous over traditional foams. Because of their easy application, foams are often utilized on the scalp or other hair-bearing areas.
Solutions are very thin and light. They are made from water, alcohol, and other liquids. Solutions come in a clear or hazy, thin-textured, liquid phase. As a result of this, they can be drying from evaporation, easy to spread, and messy to apply. Solutions are most useful for the scalp, as they can penetrate the skin through hair. Due to the presence of alcohols, they are more prone to stinging sensations when applied to inflamed skin.