lacto-

Lacto- is a combining form used like a prefix meaning “milk.” In terms from chemistry, it used to specifically mean “lactate” or “lactic acid.” It is often used in scientific and medical terms.

Lacto- comes from Latin lac (stem lact-), meaning “milk.” The Latin cognate of lac is gála (stem galakt-), also meaning “milk,” which is the source of galaxy. To learn more, check out our Words That Use articles on galacto- and galact-.

What are variants of lacto-?

When combined with words or word elements that begin with a vowel, lacto- becomes lact-, as in lactose.

A less common variant of lacto-, when combined with some words or word elements that begin with a consonant, is lacti-, as in lactifuge.

Want to know more? Read our Words That Use articles about lact- and lacti-.

One example of a scientific term that uses the form lacto- is lactogen, “an agent that stimulates lactation.”

The lacto- part of the word means “milk,” as we already know. The second part of lactogen is the combining form -gen, which means “that which produces.” Lactogen literally translates to “that which produces milk.”

What are some words that use the combining form lacto-?

• lactobacillus
• lactocele
• lactoferrin
• lactoflavin
• lactogenesis
• lactometer

What are some other forms that lacto- may be commonly confused with?

• galact-
• galacto-

The combining form -cele means “tumor.” With this in mind, what does lactocele literally mean?