Most capsule pills are made of gelatin, a protein derived from animal collagen. But a growing number use plant-based alternatives like cellulose or pullulan, a carbohydrate produced by fungal fermentation. The shell material determines not only how the capsule dissolves in your body but also whether it fits dietary or religious requirements.
Hard Gelatin Capsules
The classic two-piece capsule you twist apart is almost always made from gelatin. Gelatin comes in two types depending on how the animal collagen is processed. Type A gelatin is made by treating collagen with acid and typically comes from pigs (porcine). Type B gelatin is made through an alkaline process and usually comes from cows (bovine). Both types produce the firm, glossy shells you see on most prescription and over-the-counter medications.
Hard gelatin capsules contain a relatively high amount of moisture, around 13 to 16% of the shell’s weight. That moisture is what keeps them flexible enough to swallow without cracking. If gelatin capsules are stored in very dry conditions, they can become brittle. In overly humid environments, they may soften or stick together.
Softgel Capsules
Softgels use the same basic gelatin but with added plasticizers to make the shell pliable and chewable rather than rigid. The primary plasticizer is glycerol (glycerin). Water also plays a role during manufacturing, helping the gelatin form its structure, but most of that water evaporates during production and storage. The finished softgel shell typically retains 4 to 10% water content.
Softgels are sealed in one piece rather than fitted together like hard capsules, which makes them ideal for liquid or oil-based fills like fish oil or vitamin E. The flexible shell also makes them easier to swallow for many people.
Plant-Based Capsule Shells
If a capsule is labeled “vegetarian” or “vegan,” it’s typically made from one of two materials: HPMC or pullulan.
HPMC (hydroxypropyl methylcellulose) is the most common gelatin alternative. It’s a semi-synthetic material made from cellulose, the structural fiber in plants. During manufacturing, cellulose is treated with an alkaline base, then chemically modified so that some of its molecular groups are replaced with methyl and hydroxypropyl groups. The result is a clear, flexible film that behaves similarly to gelatin when formed into capsule shells. HPMC capsules hold much less moisture than gelatin, around 4.5 to 6.5%, which makes them less sensitive to humidity and less likely to become brittle in dry storage.
Pullulan capsules are the newer option. Pullulan is a carbohydrate polymer created entirely through fermentation. A fungus called Aureobasidium pullulans feeds on a sugar substrate, often from tapioca or corn starch syrup, and produces pullulan as a byproduct. The pullulan is then purified through filtration, decolorization, and drying. The resulting material forms a thin, oxygen-resistant film, which is why pullulan capsules are sometimes marketed for supplements sensitive to oxidation.
Some capsule manufacturers also use modified plant starches, including waxy corn starch and potato starch, to create soft vegan capsules as an alternative to gelatin-based softgels.
What Else Is in the Shell
Beyond the base material, capsule shells contain a handful of functional additives. Colorants give capsules their distinctive colors, and these can be either natural or synthetic. Natural options include curcumin (yellow), riboflavin (yellow-orange), annatto (orange-red), vegetable carbon (black), and carotenes (orange). Synthetic dyes like brilliant blue, tartrazine, and indigotine are also approved in many countries, though some have faced restrictions due to safety concerns. Colorants typically make up 0.5 to 1% of the shell’s weight.
Opacifiers make the shell non-transparent so you can’t see the powder or liquid inside. Titanium dioxide has been the standard opacifier for decades, but it’s under increasing regulatory scrutiny. The European Medicines Agency evaluated 13 titanium dioxide-free capsule shells and found that none of the white alternatives matched titanium dioxide’s opacity or mechanical strength. Red and orange capsules made with iron oxide performed well, but iron oxide has daily intake limits set by the WHO and FDA that restrict its use in medications requiring multiple daily doses. For now, replacing titanium dioxide in white capsules remains an unsolved problem for the pharmaceutical industry.
Preservatives like sorbic acid, sodium benzoate, potassium sorbate, and parabens are sometimes added in small concentrations (0.01 to 0.5%) to prevent microbial growth during storage. Parabens, typically a 4:1 blend of methyl paraben and propyl paraben at about 0.2%, are among the most common because they work across a wide pH range.
Enteric-Coated Capsules
Some capsules are designed to pass through your stomach intact and dissolve only in your intestines. These enteric-coated capsules use acid-resistant polymers layered over the shell. The coating stays intact in the acidic environment of the stomach (pH around 1 to 3) but breaks down in the more neutral environment of the small intestine (pH 5.5 to 7). This protects either the medication from stomach acid or your stomach lining from the medication. You’ll see enteric coatings on certain pain relievers, digestive enzymes, and probiotics.
Gelatin and Dietary Restrictions
Because standard gelatin capsules come from pigs or cows, they raise concerns for people following halal, kosher, vegetarian, or vegan diets. Porcine gelatin is not halal or kosher under any circumstances. Bovine gelatin can be halal if the animal was slaughtered according to Islamic law, and fish-derived gelatin is generally considered permissible. Halal certification also requires that the entire production line be physically separated from non-halal production to prevent cross-contamination.
If you need to avoid animal-derived capsules, look for labels specifying “vegetarian capsule,” “vegan capsule,” “HPMC,” or “pullulan” on the supplement or medication packaging. Many supplement brands now default to HPMC capsules, but most prescription medications still use gelatin. If you’re uncertain about a prescription, your pharmacist can check the inactive ingredient list for you.