Regular milk contains the milk sugar lactose, while lactose-free milk does not. Commercial milk producers add lactase, an enzyme that breaks down lactose, to lactose-free milk so that you can drink it without experiencing gastrointestinal symptoms. Lactase makes the milk taste sweeter. And lactose-milk also has a different shelf life than regular milk.

Lactose Content

Drinking lactose-free milk can prevent the symptoms of lactose intolerance if you're one of the approximately 30 million Americans with lactose intolerance, according to MedlinePlus. The most common symptoms include abdominal discomfort, including nausea, diarrhea, gas and bloating, which begin 30 minutes to two hours after ingesting lactose. The incidence of lactose intolerance increases as you get older; it occurs most commonly in people of African-American, Asian, Mediterranean or Native American descent. Some people can tolerate a small amount of lactose in their diet, while others can't. Lactose intolerance doesn't cause serious illness or have long-term health effects. Avoiding lactose or taking over-the-counter lactase when you eat dairy products is the only treatment necessary.

Taste Differences

Lactose-free milk tastes sweeter than regular milk because the milk sugar lactase is broken down into two simple sugars, galactose and glucose. Simple sugars taste sweeter on your tongue than complex sugars. A Kansas State University study published in the June 2009 issue of "LWT Food Science and Technology" on the characteristics of lactose-free milk reported that the sweeter, more highly processed, cooked taste of lactose-free milk might be a deterrent to consumer interest in the product.

Shelf Life

Ultra-pasteurized milk has a longer shelf life than regular milk, lasting up to 60 days compared with between seven and 16 days for regular milk, according to Strauss Family Creamery. This is a benefit for the manufacturer because lactose-free milk doesn't have as rapid a turnover on the store shelves, since there isn't as high a demand for it as for regular milk. Producers heat the milk to at least 280 degree Fahrenheit for at least two seconds. Regular pasteurized milk is heated to 170 degrees Fahrenheit for 19 seconds and then immediately cooled to 40 degree Fahrenheit or lower.

Nondairy Lactose-Free Milks