Probiotics are bacterial species that don't cause infection in humans, but instead provide some sort of benefit to the digestive tract or other organ systems. While there are some well-documented uses and benefits of probiotic organisms, scientific evidence regarding the use of probiotics in treating lactose intolerance is quite mixed.
Probiotics are defined as bacteria that benefit the host in some way. For instance, humans depend on a variety of non-pathogenic bacteria, meaning species that don't cause infection, that live in the intestine and help to maintain proper function. One of the most familiar of the probiotic species is Lactobacillus acidophilus, the species responsible for converting milk into yogurt. Lactobacillus and other probiotic bacteria are thought by some to be important components of the diet as a mechanism for improving digestive function.
Lactose intolerance is caused by limited or absent production of the enzyme that your small intestine would normally use to digest lactose, or milk sugar. In the absence of this enzyme, called lactase, you can't absorb lactose. Instead, it passes into your lower gastrointestinal tract. There, bacteria break it down and use its components for energy. This results in the production of gas, leading to the typical lactose intolerance symptoms of cramping and bloating.
There are some scientific studies that suggest consuming probiotics, especially Lactobacillus acidophilus, can help relieve the symptoms of lactose intolerance and allow you to digest milk and other dairy products more easily. For instance, a 1995 article published in the "Journal of Dairy Science" notes that children who consumed milk with Lactobacillus supplements experienced fewer symptoms of lactose intolerance than those who drank milk without probiotic supplements.
Not all scientific evidence supports using probiotics to alleviate symptoms of lactose intolerance, however. A 2005 review article published in the "Journal of Family Practice" notes that most of the research done on probiotics and lactose intolerance suggests no correlation between probiotic use and symptom relief. Most probiotics, including Lactobacillus, are quite safe, however. As such, you might want to try probiotic supplements as a method of dealing with your lactose intolerance, understanding that they might not be effective.