What Is Lactose?

Natural Sugar Found in Milk

Table of Contents
View All
Table of Contents

Lactose is a natural sugar that's found in milk. It is a carbohydrate and it is made up of two sugars: glucose and galactose. Lactose is an important source of energy for babies, and it is also commonly used in food processing and pharmaceutical drug manufacturing.

Pouring a class of milk from a pitcher
naturalbox / iStock / Getty Images 

What It Is

Lactose is one of the major components of milk. Structurally, it is a disaccharide— a sugar molecule that’s composed of two simple sugars. Glucose can be found in many other food substances, but lactose is the only known source of galactose.

Lactose is white and odorless, and you may sometimes see or hear it referred to as "milk sugar." Lactose is only found in milk from mammals, so plant-based milk products like almond milk and soy milk don’t contain it.

The enzyme lactase helps the human body digest lactose. It does this by breaking and splitting lactose into glucose and galactose, a process that prepares these sugars for use as energy by the body.


Lactose has several uses, including drug manufacturing, food processing, and fermentation.

Pharmaceutical Uses

Lactose is widely used in the pharmaceutical industry in the preparation and manufacturing of drugs. Pharmaceutical-grade lactose is produced from whey—the liquid that’s left after milk has been curdled and strained during the making of cheese.

In most of its applications, lactose is used as an excipient (inactive ingredient). Its primary purpose is to aid the delivery of the active ingredient in the body. It’s mostly used in tablets, capsules, and dry powder inhalers.

Lactose is present in about 60-70% of all pharmaceutical dosage forms—like capsules, tablets, syrups, creams, and pastes. And about 45% of drugs contain a combination of lactose and microcrystalline cellulose (MCC).

Some of the roles lactose performs in drugs are:

  • It acts as a filler: Sometimes the active ingredient in a drug is present in very small quantities. Fillers like lactose bulk up the drug, helping it flow better. Fillers also make it easier to measure the active ingredient in drugs.
  • It acts as a binder: Lactose binds pills together by helping the other ingredients in a tablet mix and stick together.

Some of the characteristics of lactose that make it work well for these purposes are its blandness, chemical and physical stability, easy availability, compatibility with active ingredients, and ability to dissolve in water. 

Pharmaceutical-grade lactose is produced and processed to meet industry purity standards.

Food Processing

Lactose is used in several facets of food processing. Edible lactose that’s used in food processing is also mostly produced from whey.

It’s used in seasonings and baked goods due to its ability to carry colors and flavors well. It’s also added to foods and edibles like ice cream, skim milk, condensed milk, dry soups, coffee creamers, chocolate and candies, meat products, and canned fruit and vegetables.

When added to food, lactose may reduce cost and regulate sweetness.


Lactose is fermented to produce foods like cheese, yogurt, kefir, and acidified (sour) milk. Lactose is also fermented to produce lactic acid, which has a number of uses in the pharmaceutical, cosmetic, and food industries.

The process of fermentation involves adding lactic acid bacteria (and less commonly, yeast) to milk or to a milk product.

Bacterial Identification

In the clinical laboratory, the ability of bacteria to ferment lactose might help differentiate which bacterial species is causing an infection, such as food poisoning. For example, Escherichia coli ferments lactose while most Salmonella species do not.

Cutting Agent

Lactose is commonly used as a cutting agent for illegal recreational drugs. Cutting agents are chemicals or drugs that are used to dilute and add bulk to recreational drugs.

The use of cutting agents is prevalent in illegal drug production, and the substances used for this process are typically less expensive than the recreational drug itself.

Health Benefits

Lactose has some health benefits for babies. Human breast milk is composed of 7.2% lactose, and this sugar provides up to half of the energy needs of breastfeeding babies. 

The lactose found in human milk has a beneficial effect on the development of microorganisms that live in the digestive tract of babies. It also helps babies absorb calcium better.

Lactose Intolerance

Lactose intolerance is when your body is unable to break down and digest lactose that's consumed in milk and other dairy products. The condition usually causes stomach discomfort.

Normally, lactase enzymes help to break down lactose. But when the body doesn’t produce enough lactase, you can have lactose intolerance. Lactose intolerance is very common, and it causes symptoms like bloating, diarrhea, cramps, and flatulence after consumption of dairy products that contain lactose.

Lactose intolerance is somewhat different from lactose maldigestion. With lactose maldigestion, the activity of the lactase enzyme is reduced—making lactose digestion difficult. But it causes little or no symptoms at all.

Lactose maldigestion affects 70-75% of people in the world.

Some babies are born with a lactase deficiency and cannot digest lactose in breast milk or formula. Severe diarrhea is the major symptom of this kind of lactose intolerance, and babies with this condition may develop dehydration and weight loss. Often, lactose-free formula is recommended.

A Word From Verywell

Lactose is a natural sugar that's present in dairy foods. It also has a number of uses in the food processing and pharmaceutical industries. While lactose has many health benefits for babies in their development stage, adults can do without it. So if you find that you’re lactose intolerant, you can avoid lactose-containing foods without the fear of adverse health effects due to lactose deficiency. Instead, look for foods that are labeled lactose-free or lactose-reduced. But keep in mind that there are other important components of dairy products—such as calcium and protein—that you need to make sure you are getting in adequate amounts.

Frequently Asked Questions

  • What are the benefits of lactose-free milk?

    The main benefit in lactose-free milk is allowing people with lactose intolerance to enjoy milk and dairy products without triggering uncomfortable symptoms. However, it may also benefit people without a lactose intolerance, since lactose-free milk contains fewer added sugars and a lower calorie count.

  • What are the symptoms of lactose intolerance?

    The symptoms of lactose intolerance include bloating, gas, diarrhea, nausea, and stomach cramps or pain. These symptoms and their severity will differ among people with lactose intolerance. Symptoms usually occur within 30 minutes to two hours after ingesting lactose.

  • Does milk powder have lactose?

    Yes, milk powder (powdered milk) does have lactose. However, there are low-lactose varieties of milk powder that allow people with lactose intolerance to safely use them. These products will say "lactose-free" on the packaging.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hebbink G, Dickhoff B.. Application of lactose in the pharmaceutical industry. Lactose. 2019;175-229. doi:10.1016/B978-0-12-811720-0.00005-2

  2. American Society for Microbiology. The Origin of MacConkey Agar.

  3. U.S. National Library of Medicine Genetics Home Reference. Lactose Intolerance.

  4. Dekker PJT, Koenders D, Bruins MJ. Lactose-Free Dairy Products: Market Developments, Production, Nutrition and Health BenefitsNutrients. 2019;11(3):551. doi:10.3390/nu11030551

  5. Johns Hopkins Medicine. Lactose Intolerance.

Additional Reading

By Tolu Ajiboye
Tolu Ajiboye is a health writer who works with medical, wellness, biotech, and other healthcare technology companies.