What Is Lactose?

Natural Sugar Found in Milk

Lactose is a type of sugar found in milk

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In This Article

Lactose is a natural sugar that's found in milk. It is a carbohydrate and is made up of two sugars called 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.

What It Is

Lactose is one of the major components of milk. Structurally, it is a disaccharide— a sugar that’s composed of two simple sugars. Glucose and galactose are the two simple sugars that make up lactose. 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 like almond milk and soy milk don’t contain it.

The enzyme lactase helps the human body digest lactose. It does this by breaking splitting lactose into glucose and galactose, after which these sugars then can be used directly 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. 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.

About 45% of drugs contain a combination of lactose, and another chemical called, microcrystalline cellulose (MCC). Other studies report higher numbers, estimating that lactose is present in about 60-70% of all pharmaceutical dosage forms like capsules, tablets, syrups, creams, and pastes. 

Some of the functions lactose performs in drugs are:

  • It acts as a filler. Sometimes the active ingredient in a drug is present in quantities that are too small to handle. Fillers like lactose bulk up the drug, making it flow better. Fillers also make it easier to measure the active ingredient in drugs.
  • It acts as a binder. Lactose binds pills together. That is, it helps 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 stability, physical stability, easy availability, compatibility with active ingredients and ability to dissolve in water, 

The lactose used in these applications is pharmaceutical-grade and has been produced to meet purity standards laid down by regulators in the industry. Pharmaceutical-grade lactose is produced from whey—the liquid that’s left after milk has been curdled and strained during the making of cheese.

Food Processing

Lactose is used in food processing for many purposes. For one, it’s used in seasonings and baked goods for 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.

Lactose is added to these foods to reduce cost and regulate sweetness, among other reasons. Edible lactose that’s used in food processing is also mostly produced from whey.


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 the milk or milk product.

Bacterial Identification

In the clinical laboratory, the ability of bacteria to ferment lactose or not is a typical part of identifying bacteria, especially those found in the intestinal tract. This differentiates which bacterial species is causing an infection or 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 illicit 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 and the substance is typically less expensive than the recreational drug itself.

Health Benefits

Lactose has some health benefits for babies. Human breast milk is 7.2% lactose, and it provides for up to half of the energy needs of breastfeeding babies. The lactose found in human milk also has a positive effect on the 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 in milk and other dairy products, and you experience stomach discomfort as a result.

Normally, an enzyme called lactase helps to break down lactose. But when the body doesn’t produce enough lactase anymore, an intolerance develops. Lactose intolerance is very common, and people with it experience symptoms like bloating, diarrhea, cramps, and flatulence when they consume 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. In a way, you could say that lactose intolerance is lactose maldigestion that causes symptoms.

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

Some babies are born with a lactase deficiency, and so cannot digest lactose in breast milk or formula. Severe diarrhea is the major symptom of this kind of lactose intolerance, and an affected baby may develop severe dehydration and weight loss if not fed lactose-free formula.

A Word From Verywell

Lactose is a natural sugar with many different uses in the food processing and pharmaceutical industries. While lactose has many health benefits for babies in their development stage, many adults can do without it. So if you find that you’re lactose intolerant, you can avoid foods with lactose without the fear of any possible health risks. Instead, look for foods that are labeled lactose-free or lactose-reduced.

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Article Sources
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  2. Smith KP. The origin of MacConkey agar. American Society for Microbiology. October 14, 2019.

  3. U.S. National Library of Medicine Genetics Home Reference. Lactose intolerance. Updated August 17, 2020.

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