lac·​tose | \ ˈlak-ˌtōs How to pronounce lactose (audio) , -ˌtōz\

Definition of lactose

: a disaccharide sugar C12H22O11 that is present in milk and yields glucose and galactose upon hydrolysis and yields especially lactic acid upon fermentation

Examples of lactose in a Sentence

Recent Examples on the Web

In general, fresher cheeses contain more lactose than aged cheeses, which means cheeses like feta and ricotta, my old favorites, are higher in lactose, and now my enemy. Christian Allaire, Vogue, "I Gave Up Dairy—And My Adult Acne Vanished in Under a Month," 28 July 2018 IPAs brewed with lactose for extra body have also started to multiply (after Tired Hands became the first local to make it). Craig Laban,, "2018 Brewvitational standouts: Peter, haze and pucker," 10 May 2018 The process of fermenting milk into cheese also reduces its lactose content, because much of it drains away with the liquid whey. Kiona N. Smith, Ars Technica, "Early cheese making may have helped lactose-intolerant farmers spread," 14 Sep. 2018 Polar bear milk has almost ten times as much fat and protein as cow's milk, almost no lactose. Bob Gathany,, "Up in the air at the Huntsville Community Kite Festival," 4 Mar. 2018 To make it, dairy producers have long employed the help of Streptococcus thermophilus, a bacteria that gobbles up the lactose in milk and poops out lactic acid. Megan Molteni, WIRED, "The WIRED Guide to Crispr," 27 Apr. 2018 Glutard, then, is a disparaging term for a person who doesn’t eat gluten, lactard for someone who can’t tolerate lactose, and libtard for a liberal. Melissa Mohr, The Christian Science Monitor, "When good words turn bad," 28 June 2018 Nut and seed milks are a delicious lactose-free alternative to traditional dairy milk, and they can be used in a variety of recipes that require the real thing. Time, "Weekend Recipe: Your Guide to Creating Dairy-Free Nut, Seed and Rice Milks," 22 June 2018 The cholesterol-free rolls are entirely vegan, with no use of dairy, lactose or eggs, the release said. Wesley Case,, "Vegan bakery Cinnaholic to open in Hampden in early June," 23 May 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'lactose.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of lactose

1847, in the meaning defined above

History and Etymology for lactose

International Scientific Vocabulary

Keep scrolling for more

Learn More about lactose

Statistics for lactose

Last Updated

23 Apr 2019

Look-up Popularity

Time Traveler for lactose

The first known use of lactose was in 1847

See more words from the same year

Keep scrolling for more

More Definitions for lactose



English Language Learners Definition of lactose

chemistry : a type of sugar that is present in milk


lac·​tose | \ ˈlak-ˌtōs How to pronounce lactose (audio) \

Kids Definition of lactose

: a sugar that is found in milk


lac·​tose | \ ˈlak-ˌtōs, -ˌtōz How to pronounce lactose (audio) \

Medical Definition of lactose

: a disaccharide sugar C12H22O11 that is present in milk, yields glucose and galactose upon hydrolysis, yields especially lactic acid upon fermentation, and is used chiefly in foods, medicines, and culture media (as for the manufacture of penicillin)

called also milk sugar

More from Merriam-Webster on lactose

Rhyming Dictionary: Words that rhyme with lactose Encyclopedia article about lactose

Comments on lactose

What made you want to look up lactose? Please tell us where you read or heard it (including the quote, if possible).


to speak slightingly about or to degrade

Get Word of the Day daily email!

Test Your Vocabulary

Challenging Vocabulary Quiz Returns!

  • stylized drawing of woman pole vaulting across gap to get trophy
  • Which is a synonym of fuliginous?
Name That Thing

Test your visual vocabulary with our 10-question challenge!


Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!