A base cream is a plain, unmedicated cream that serves two purposes: it works as a moisturizer on its own, and it acts as a vehicle for delivering active ingredients into the skin. Pharmacists use base creams to mix custom medications, while dermatologists recommend them as standalone emollients for dry or sensitive skin. The cream itself contains no therapeutic drug. It’s the foundation that everything else gets added to.
How a Base Cream Is Made
At its simplest, a base cream is an emulsion of oil and water held together by an emulsifier. Water typically makes up about 60 to 70 percent of the formula, while the oil phase (often olive oil, liquid paraffin, or similar lipids) accounts for roughly 20 to 25 percent. The emulsifier, which prevents the oil and water from separating, makes up the remaining few percent. Thickeners like cetyl alcohol or xanthan gum give the cream its body, and a small amount of preservative keeps bacteria and mold from growing.
One of the most widely recognized formulas is Aqueous Cream BP, standardized in the British Pharmacopoeia. It contains 6 percent liquid paraffin, 15 percent white soft paraffin, purified water, emulsifying wax (a blend of cetostearyl alcohol and sodium lauryl sulfate), and a preservative called chlorocresol at 0.1 percent. This formula has been used for decades in hospitals and pharmacies as both a moisturizer and a compounding base.
Oil-in-Water vs. Water-in-Oil
Base creams fall into two main categories depending on how the oil and water are arranged. In an oil-in-water (O/W) cream, tiny oil droplets are suspended in a water phase. These creams feel lighter, absorb quickly, and leave less of an oily residue. Most moisturizers and topical steroid creams use an O/W base.
In a water-in-oil (W/O) cream, the arrangement is reversed: water droplets sit inside a continuous oil phase. These creams feel richer and greasier. They’re better at locking in moisture because the outer oil layer creates a stronger seal over the skin. W/O bases tend to work well for very dry or sensitive skin, and they’re common in sunscreens and heavier cosmetic formulations. The choice between the two depends on what the cream needs to do and where on the body it will be applied.
Why It Matters as a Drug Delivery Vehicle
In compounding pharmacies, the base cream is far more than a filler. It controls whether an active drug actually reaches the skin and how much gets absorbed. The base must release the drug from its structure so the medication can penetrate the outer skin layer and reach its target. A poorly chosen base can trap the drug inside the cream, making the medication essentially useless.
The formulation process is surprisingly sensitive. Changing even one variable, such as how long the mixture is blended or the order in which drugs are added, alters the cream’s internal structure. Those structural differences lead to measurable changes in how much drug the skin absorbs. This is why compounding pharmacists follow precise protocols and why switching between base creams for the same medication can produce noticeably different results.
How It Protects the Skin on Its Own
Even without any added medication, a base cream functions as an emollient. It creates a thin oily film on the skin’s surface that traps moisture underneath, preventing water from evaporating through the outer skin layer. This occlusive effect is especially valuable for people with eczema or chronically dry skin, where the natural skin barrier is already compromised.
By restoring that barrier, the cream does more than just hydrate. It helps block irritants, allergens, and bacteria from penetrating the skin, which can reduce flare-ups and lower the risk of infection. Some base cream formulas also include humectants like glycerin, which actively pull water from deeper skin layers up into the surface layer, adding a second moisturizing mechanism on top of the protective film.
The Sodium Lauryl Sulfate Concern
Not all base creams are equally gentle. Sodium lauryl sulfate (SLS), a surfactant used in some formulations including Aqueous Cream BP, is a well-documented skin irritant. It helps blend the oil and water phases together, but on damaged or sensitive skin it can cause stinging, redness, and dryness. For people with eczema, using an SLS-containing base cream as a leave-on moisturizer can actually worsen the condition it’s meant to soothe.
If you have sensitive or broken skin, look for base creams that use nonionic emulsifiers instead. Cetomacrogol cream, for example, uses a polyethylene glycol-based emulsifier that tends to be much gentler. Other alternatives rely on plant-derived emulsifiers like cetearyl glucoside or methyl glucose sesquistearate. Your pharmacist can help identify which base cream avoids the ingredients most likely to irritate your skin.
Storage and Shelf Life
Unmedicated base creams generally last a few years from the date of purchase, though the container type matters more than most people realize. Tubs with screw-top lids expose the product to air every time you open them, which accelerates breakdown. Tubes are somewhat better, and pump bottles (especially vacuum pumps that prevent air from entering) offer the longest shelf life.
Store base creams at a stable, cool temperature. Heat breaks down the emulsion over time, which can cause the oil and water phases to separate. If your cream changes texture, develops an unusual smell, or looks different from when you bought it, discard it. Labeling the container with the date you opened it is a simple way to keep track, since many base creams don’t print a clear expiration date on the packaging.