Calamine lotion is a simple suspension you can mix at home using just five ingredients. The standard formula from the United States Pharmacopoeia (USP) combines calamine powder, zinc oxide, glycerin, bentonite magma, and calcium hydroxide solution (lime water) to create the familiar pink, chalky liquid that soothes itchy skin. Because the active ingredients are mineral powders suspended in liquid rather than dissolved, calamine is classified as a “shake lotion,” which is why you always shake the bottle before use.
The Standard USP Formula
The official USP recipe produces 100 ml of calamine lotion. Here’s what goes into it:
- Calamine powder: 8 grams
- Zinc oxide powder: 8 grams
- Glycerin: 2 ml
- Bentonite magma: 25 ml
- Calcium hydroxide solution (lime water): enough to bring the total volume to 100 ml
This version contains no phenol, making it a “bland” calamine lotion. Some commercial formulations, particularly those following the British Pharmacopoeia, include a small amount of liquified phenol for extra itch relief, but the USP version skips it entirely.
What Each Ingredient Does
Calamine itself is simply zinc oxide tinted pink with a small amount of iron oxide. That means this formula actually contains two forms of zinc oxide: the tinted calamine and additional pure zinc oxide. Together, they make up 16% of the final product. When the lotion dries on your skin, the zinc oxide forms a thin protective layer that absorbs moisture from weepy rashes, cools the skin through evaporation, and creates a mild barrier against further irritation.
Glycerin acts as a humectant, keeping the lotion from drying out your skin too aggressively and giving it a smoother feel on application. Bentonite magma is a thick clay gel that serves as the suspending agent. Without it, the heavy zinc oxide and calamine powders would settle to the bottom almost instantly and be difficult to re-mix. The bentonite keeps the particles distributed more evenly throughout the liquid. Calcium hydroxide solution, or lime water, is the liquid base. It’s mildly alkaline, which helps soothe inflamed skin and contributes to the lotion’s drying action on oozing rashes like poison ivy.
Step-by-Step Mixing Process
Start by weighing out 8 grams each of calamine powder and zinc oxide powder into a clean mortar or mixing bowl. Add the 2 ml of glycerin to the powders and mix thoroughly using a pestle or small spatula. The glycerin helps wet the powders and prevents clumping. You want a smooth, uniform pink paste with no dry lumps.
Next, slowly add small portions of the bentonite magma to the paste, mixing well after each addition until all 25 ml is incorporated. Work slowly here. Adding too much at once makes it harder to get a smooth consistency. Once the paste and bentonite are fully blended, gradually stir in the calcium hydroxide solution, a little at a time, until the total volume reaches 100 ml. Pour the finished lotion into a clean glass or plastic bottle with a tight-fitting cap.
If you don’t have a graduated cylinder to measure the final volume precisely, you can pre-measure 100 ml of water in your bottle, mark the level, then use that as your reference when adding the lime water at the end.
Where to Find the Ingredients
Calamine powder and zinc oxide powder are available from pharmacist supply companies, soap-making suppliers, and online retailers that sell cosmetic-grade raw materials. Look for USP-grade versions to ensure purity. Bentonite magma is a 5% bentonite clay gel in water. You can buy pre-made bentonite magma from compounding suppliers, or make your own by slowly sprinkling 5 grams of bentonite clay into 95 ml of hot water and letting it hydrate for 24 hours until it forms a thick, smooth gel.
Calcium hydroxide solution is made by adding excess food-grade calcium hydroxide (also sold as “pickling lime” or “slaked lime”) to distilled water, shaking it, and letting it settle. The clear liquid you pour off the top is your lime water. It’s a saturated solution, meaning only a small amount of calcium hydroxide actually dissolves. You can also find pre-made lime water from compounding pharmacies.
Storage and Shelf Life
Because calamine lotion contains water-based ingredients, it can support bacterial and mold growth over time. The USP formula doesn’t include a preservative, so homemade calamine lotion should be stored in a cool, dry place and used within a few weeks. Refrigeration can extend its usable life slightly. If you notice any off smells, color changes, or visible mold, discard the batch.
The lotion will naturally separate between uses as the mineral powders settle. This is completely normal and expected. Shake the bottle vigorously before every application to redistribute the active ingredients evenly.
How to Apply It
Shake the bottle well. Clean the affected area with soap and water and let the skin dry completely. Then apply a thin layer of lotion using a cotton ball, cotton pad, or soft cloth. Let it dry on the skin. You can reapply as often as needed for comfort. The lotion works best on surface-level irritations: poison ivy, oak, and sumac rashes, insect bites, mild sunburn, and other conditions where the skin is itchy or oozing. Avoid applying it to deep wounds, animal bites, or severe burns. Keep it away from your eyes.
For children under six months old, calamine lotion generally isn’t recommended without professional guidance. For older children and adults, there’s no strict limit on how often you can apply it. If the irritation hasn’t improved within seven days, or if it clears up and then comes back, that’s a sign something else may be going on.
Scaling the Recipe
The USP formula scales easily. To make a smaller 50 ml batch, simply halve everything: 4 grams calamine, 4 grams zinc oxide, 1 ml glycerin, 12.5 ml bentonite magma, and enough lime water to reach 50 ml. Smaller batches make more sense for home use since you’ll use the lotion up before any preservation concerns arise. If you want a larger supply, double the original recipe to 200 ml, but keep in mind that without a preservative, making more than you’ll use in a few weeks means risking spoilage.