The Latin term for milk is lac lactis. Because Latin was the international language of science for many centuries, especially during the centuries that our modern vocabulary for science was developed, any white fluid, or chemical that was discovered in a white fluid, had a "lact" put into its name.
I have a page on my website, Dairy or Nondairy? The Experts Speak, that discusses many of the "lact" words that are used in foods, such as lactate, lactylate, and lactic acid. There is absolutely no lactose in any of those chemicals.
You can also find "lact", not surprisingly, in milk proteins. Lactalbumin and lactoglobulin are two members of the whey family of proteins. They have no lactose, but people with protein allergies should avoid them.
That doesn't even begin to cover the "lact" terms, but I don't discuss the rest because they are not food additives and so there's no reason even to mention them, normally.
However, people trying to protect their loved ones are rightfully suspicious of every word that comes before them.
I found this question on an Alzheimer's question site:
My wife has been having severe memory lapses, refuses to go to doctor so I have begun reading up on Alzheimer's.... Here's the question: Just found out that lactacystin is an inhibitor of proteosome activity and may therefore be related to experimentally induced Alzheimers. The chemical structure is an odd one and I have, as I've mentioned, no access to scientific literature which would help me determine why the "LACTA" in the name. Perhaps coincidentally my wife has been abusing lactase tablets during the time she has developed AZ symptoms.
Could there be any connection? Even if a long shot I' ll have her discontinue lactase and got for soy milk products, etc.
There is no connection at all. Lactacystin is a cyclic amide, which is also known as a lactam. Lactam is a shortening of lactone + amide. A lactone is a cyclic ester, a type of lactide, which is formed from dehydrated lactic acid. And lactic acid was first found in soured milk.
Neither lactase nor lactose have any chemical similarity to any of these chemicals.
Nor is it possible to abuse lactase tablets. There are no known side effects to lactase. Any unused lactase passes out of the body with other waste. So does used lactase, for that matter. Lactase is a catalyst, a substance that speeds up reactions without being consumed in them. It works in the intestines but is not absorbed by the body.
I left a brief version of this information on that Alzheimer's site. While asking the question is always good, in this particular case "a little knowledge is a dangerous thing" was the cause of needless worry.