Most vitamin capsules are made of gelatin, a protein derived from animal collagen. The shell you swallow is essentially processed animal skin or bone that has been formed into a thin, dissolvable casing. Vegetarian alternatives exist, typically made from modified plant cellulose, and a newer option uses fermented tapioca starch. Beyond the shell itself, capsules also contain inactive filler ingredients that help the vitamin powder flow evenly during manufacturing.
Gelatin: The Most Common Shell Material
Gelatin capsules dominate the supplement market. The gelatin comes from three main sources: pig skin (about 46% of global production), cattle hides (about 29%), and a mix of pig and cattle bones (about 23%). Fish gelatin accounts for less than 1.5% of total production.
To make gelatin, manufacturers extract collagen from animal skin or bone using acid or alkaline baths followed by heat treatments. The thermal process separates the protein from everything else in the raw material. This produces two types of gelatin: Type A from acid processing and Type B from alkaline processing. The resulting protein dissolves reliably in the warm, wet environment of your digestive tract, which is why it has been the default capsule material for decades.
Hard gelatin capsules are made by dipping cold metal pins into hot gelatin solutions. The gelatin sets around the pins, forming two interlocking halves (a body and a cap) that are later filled with powdered vitamins and snapped together. These capsules need to maintain a moisture content between 13% and 16% to stay functional. If they dry out below that range, they become brittle and crack. If they absorb too much moisture from humid storage or from their own contents, they soften and stick together.
Softgel Capsules Work Differently
Softgels, the smooth, one-piece capsules often used for fish oil and vitamin D, are also gelatin-based but have a fundamentally different construction. Their shells contain gelatin, water, and a plasticizer that keeps them flexible. Water makes up 30 to 40% of the wet shell formula during manufacturing but evaporates down to just 4 to 10% in the finished product. Because water alone can’t keep the shell pliable long-term, manufacturers add a non-volatile plasticizer at 15 to 30% of the shell formula.
Glycerin is the most widely used plasticizer, valued for its strong interaction with gelatin and low tendency to evaporate. It works especially well for capsules filled with oil-based vitamins. The tradeoff is that glycerin-plasticized shells are more permeable to oxygen and less resistant to moisture, which can affect shelf life. Sorbitol is the other common plasticizer, preferred when the fill contains ingredients that might migrate into the shell. Sorbitol doesn’t interact with gelatin directly but instead works by retaining moisture. In very dry storage conditions, though, sorbitol can crystallize and make the shell fragile.
Unlike hard capsules, which are filled and sealed in separate steps, softgels are formed, filled, and sealed all at once. In the most common method (the rotary die process), two ribbons of plasticized gelatin flow over rotating rollers with capsule-shaped cavities. The fill is injected between the ribbons, and the rollers press together to seal and cut each capsule simultaneously.
Plant-Based Capsule Options
If you see “vegetarian capsule” or “vegan capsule” on a supplement label, the shell is almost certainly made from hydroxypropyl methylcellulose, commonly abbreviated as HPMC. This material starts as cellulose, the structural fiber in plant cell walls, which is then chemically modified to make it water-soluble. The process involves treating cellulose with an alkaline base, then reacting it with two chemicals that attach new molecular groups to the cellulose chain. The result is a semi-synthetic polymer that can form capsule shells with properties similar to gelatin.
HPMC capsules are free of animal products, preservatives, allergens, starch, and gluten. They also handle moisture differently than gelatin. While gelatin capsules need 13 to 16% moisture to avoid cracking, HPMC capsules stay stable at much lower levels, between 2 and 6%. This makes them a better match for moisture-sensitive vitamin formulations, since there’s less risk of water migrating from the shell into the powder inside.
A newer alternative is pullulan, a polysaccharide produced by fermenting tapioca starch. Pullulan capsules are vegan, non-GMO, and gluten-free. Their standout feature is oxygen barrier performance. Compared to both HPMC and gelatin, pullulan shells let the least oxygen through, which helps protect vitamins prone to oxidation (like vitamin C or certain B vitamins) from degrading on the shelf.
What’s Inside Besides the Vitamin
The vitamin itself rarely fills the entire capsule. Manufacturers add inactive ingredients called excipients to ensure the powder flows consistently into each capsule during high-speed production and that every capsule contains a uniform dose. Common fillers include microcrystalline cellulose (derived from wood pulp), calcium carbonate, lactose, and various sugars like glucose or sucrose.
Magnesium stearate is one of the most frequently listed inactive ingredients. It acts as a lubricant, preventing the powder from sticking to manufacturing equipment. You’ll also sometimes see rice flour, silicon dioxide (an anti-caking agent), or food starch listed on the label. These ingredients are present in tiny amounts relative to the active vitamin and are classified as Generally Recognized as Safe by the FDA, meaning they have an established safety record either through scientific testing or through a long history of use in food.
Enteric-Coated Capsules
Some vitamin capsules have an additional acid-resistant coating designed to prevent the capsule from dissolving in your stomach. Instead, the capsule passes through intact and opens in the small intestine, where absorption conditions are better. This is common for probiotics, certain enzymes, and vitamins that can cause nausea when released in the stomach. One of the most established coating materials is cellulose acetate phthalate, a polymer that has been used in pharmaceuticals for over four decades. It remains solid in acidic stomach conditions but dissolves once it reaches the more alkaline environment of the small intestine.
How to Tell What Your Capsule Is Made Of
The capsule shell material is listed in the “Other Ingredients” or “Inactive Ingredients” section of the supplement label. Gelatin will simply be listed as “gelatin” or “bovine gelatin.” Vegetarian capsules typically appear as “vegetable capsule,” “hypromellose,” or “HPMC.” Pullulan capsules are labeled as “pullulan.” If the label doesn’t specify the source, the capsule is most likely standard gelatin.
For people avoiding animal products, pork, or beef for dietary or religious reasons, the source matters. Since pig skin accounts for nearly half of all gelatin production, a capsule labeled simply “gelatin” without specifying bovine or fish origin may well contain pork-derived material. Halal and kosher-certified supplements will specify their gelatin source or use plant-based shells. If you have allergies, note that while capsule shells themselves are generally allergen-free, fillers inside the capsule occasionally contain corn-derived starch or lactose (a milk sugar), both of which will appear on the ingredient list.