lactose

noun

lac·​tose ˈlak-ˌtōs 

-ˌtōz

: 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

The undigested lactose causes symptoms.1 Newborns and babies can usually digest lactose, but this ability decreases over time. —Amber J. Tresca, Verywell Health, 19 May 2025

Chemicals used for white smoke: potassium chlorate, lactose and rosin – a natural amber resin from conifers. —Lauren Kent, CNN Money, 7 May 2025

The infection damages the gut lining, which leads to a lack of lactase, the enzyme that breaks down lactose. —Adrianna Rodriguez, USA Today, 29 Apr. 2025

Cottage cheese contains nearly 300% more lactose than Greek yogurt, so people with lactose intolerance may be able to tolerate Greek yogurt but not cottage cheese.98 Greek yogurt and cottage cheese are not appropriate for people following certain dietary patterns, such as vegan and paleo diets. —Jillian Kubala, Health, 4 Mar. 2025

Word History

Etymology

International Scientific Vocabulary

First Known Use

1847, in the meaning defined above

Phrases Containing lactose

• lactose intolerant

Rhymes for lactose

• galactose

Kids Definition

lactose

noun

lac·​tose ˈlak-ˌtōs 

: a sugar present in milk that breaks down to give glucose and galactose and on fermentation gives especially lactic acid

called also milk sugar

Medical Definition

lactose

noun

lac·​tose ˈlak-ˌtōs, -ˌtōz 

: 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