Lactase is an enzyme used to break down lactose, the natural sugar in milk and dairy products. Its primary use is helping people with lactose intolerance digest dairy without the bloating, gas, cramps, and diarrhea that come from undigested lactose sitting in the gut. About 68% of the world’s population has some degree of lactose malabsorption, making lactase one of the most widely used digestive enzyme supplements. Beyond the supplement aisle, lactase is also the key ingredient food manufacturers use to produce lactose-free milk, cheese, and other dairy products.
How Lactase Breaks Down Lactose
Lactose is a double sugar, meaning it’s two smaller sugars (glucose and galactose) bonded together. Your small intestine can only absorb single sugars, so lactose needs to be split apart before your body can use it. Lactase does exactly that: it cuts the chemical bond holding the two sugars together, releasing glucose and galactose for absorption through the intestinal wall.
When your body doesn’t produce enough lactase on its own, intact lactose travels further down into your large intestine. Bacteria there ferment it, producing hydrogen gas and drawing extra water into the colon. That fermentation is what causes the familiar symptoms of lactose intolerance: bloating, cramping, gas, gurgling sounds, and diarrhea. Taking supplemental lactase or consuming lactose-free products prevents this chain reaction by ensuring the lactose gets broken down before it ever reaches those bacteria.
Lactase Supplements for Lactose Intolerance
The most common use of lactase is as an over-the-counter supplement taken with meals that contain dairy. Products like Lactaid come in tablets ranging from about 3,000 to 9,000 FCC units (a standardized measure of enzyme activity). You take them right as you start eating, so the enzyme is present in your stomach when the lactose arrives. The enzyme works on contact, mixing with the food and splitting lactose as digestion proceeds.
Clinical trials using a crossover design, where the same patients receive both lactase and a placebo at different visits, show clear benefits. In one controlled study, lactase reduced hydrogen levels in breath tests by 55% compared to placebo over three hours. Breath hydrogen is a direct marker of undigested lactose fermenting in the gut, so that reduction reflects genuinely better digestion. Symptom scores, covering abdominal pain, bloating, flatulence, and diarrhea, dropped by 45% to 88% across trials. The improvements were statistically significant at nearly every time point measured, from 60 minutes after eating all the way through 180 minutes.
The results are meaningful but not perfect. Lactase supplements reduce symptoms rather than eliminating them entirely, and the degree of relief varies from person to person. The amount of lactose in the meal matters too. A glass of milk contains roughly 12 grams of lactose, while a slice of aged cheddar has almost none. Matching your dose to the lactose load gives you the best chance of staying comfortable.
Lactase Drops for Infant Colic
A newer application involves adding lactase drops to breast milk or formula before feeding infants with colic. The idea is that some colicky babies may be struggling with temporary lactose malabsorption, and pre-digesting the lactose could reduce their distress. A randomized, double-blind trial tested this by giving lactase drops or a placebo to infants over four weeks.
By week four, infants receiving lactase cried or fussed for an average of about 90 minutes per day, compared to nearly 180 minutes in the placebo group. Crying time alone (excluding fussing) was cut roughly in half: about 50 minutes per day versus 100 minutes. The number of days with prolonged colic episodes also dropped significantly. These results suggest lactose malabsorption plays a real role in at least some cases of infant colic, though not every baby with colic will respond to lactase.
How Lactose-Free Foods Are Made
Every carton of lactose-free milk on grocery store shelves was made using lactase. Manufacturers add the enzyme directly to regular milk and give it time to break down the lactose before packaging. The result is milk that tastes slightly sweeter, because glucose and galactose are each sweeter than lactose, but is otherwise nutritionally identical. The same process applies to lactose-free yogurt, ice cream, and cream cheese.
Most production uses “free” enzyme, meaning lactase dissolved directly into the milk. Some newer methods immobilize the enzyme inside a gel-like material so it can be reused across multiple batches, lowering costs. This approach also opens the door to controlled-release capsules, where the enzyme gradually releases inside the digestive tract rather than all at once.
The lactase used in both supplements and food manufacturing comes from microbial sources. The FDA recognizes enzyme preparations derived from the yeast Kluyveromyces lactis and from mold species like Aspergillus oryzae as safe for food use. These organisms are grown in controlled fermentation and the enzyme is extracted and purified before being added to products.
Safety and Rare Allergic Reactions
Lactase supplements have an excellent safety profile for the vast majority of people. They’ve been sold over the counter for decades and are not known to cause common side effects. However, because many commercial preparations are derived from Aspergillus mold, there is a small risk of allergic reactions in sensitized individuals.
Case reports describe reactions ranging from mouth and throat swelling to, in one documented case, full anaphylaxis with throat constriction and difficulty breathing after a first dose of a lactase tablet. Occupational exposure to lactase powder in pharmaceutical manufacturing has also been linked to asthma, nasal symptoms, and contact skin reactions in workers. These events are rare, but if you have a known mold allergy or experience any swelling or breathing difficulty after taking a lactase supplement, stop using it and seek medical attention. Some people with mold sensitivities may tolerate yeast-derived lactase preparations better, since the source organism is different.